Blueberry Lemon Mousse Cake combines lemon sponge, blueberry gelée, and an airy mousse to create a beautiful cake that’s perfect for summer celebrations.
This post has been in the hopper for months and I’m just now getting around to writing. I made this Blueberry Lemon Mousse Cake with Mirror Glaze back in April as part of my 2020 Baking Bucket List and also as my own birthday cake (happy 33 years to me!).
Find my 2019 Baking Bucket List here.
Blueberry Lemon is one of my favorite flavor combinations. I love the sweet-tart flavor and the beautiful purple-yellow pairing when blueberry and lemon are mixed in baked goods. Except, in my world, the flavors have to be strong. I’m the type that wants to KNOW there’s blueberry AND lemon in my cake.
Check out my other birthday cakes here and here.
This Blueberry Lemon Mousse Cake with Mirror Glaze has four unique components and requires about 2-days to prepare since after making the lemon sponge, blueberry gelée, and blueberry lemon mousse, you have to let the cake freeze overnight to set before finishing the cake with the mirror glaze. So plan accordingly.
Lemon Sponge
This cake starts with a very delicate lemon sponge. It’s quite thin, very delicate, and full of lemon flavor. I amped up the lemon juice and zest in the sponge to ensure the lemon flavor wasn’t missed. You bake the sponge in a large 8×8 inch pan then use a 6-inch ring to cut out the base cake layer. I attempted to bake the sponge originally in a 6-inch cake pan but as the cake cooled it shrunk leaving me with a much smaller cake.
So please, follow the instructions and cut the cake to size once baked.
Blueberry Gelée
Blueberry Gelée is just a fancy word for jelly. And to be honest, you could probably skip this if you wanted to. Personally, I don’t think it added much flavor to the overall cake but it does create a beautiful, deep purple layer in the cake once cut that’s quite striking. Your call here.
Similar to how I cut the sponge to size, you use a 4 or 5-inch ring to cut the gelée to size after it’s set.
Blueberry Lemon Mousse Cake with Mirror Glaze
This mousse, in my opinion, is the star of the cake. It’s silky, creamy, sweet, and tart. Absolutely delicious and encompasses the entire blueberry lemon flavor. For this layer of the cake, you make your mousse, assemble the cake with the sponge and gelée, then pipe the mousse on top of the sponge and gelée. You then let the mousse set overnight in the freezer in the 6-inch mold surrounded by acetate.
The next day you remove the mold and have a perfectly round, frozen cake that you can then cover in a mirror glaze.
Mirror Glaze
Mirror glaze looks quite difficult to make but to be honest, more than skill, it requires patience. Patience because while you may be tempted to immediately pour the glaze on top of your cake, you MUST wait until it is 95 degrees Fahrenheit before pouring or it will not form a thick enough layer to cover the outsides of the cake and will simply drip straight off.
While this Blueberry Lemon Mousse Cake with Mirror Glaze is a labor of love, it was 100% worth it. It was delicious, not too sweet nor too tart, and the mousse was to die for. It’s something I’d make again for a special occasion — probably my own birthday again next year!
- 1½ cups fresh blueberries
- ¼ cup granulated sugar
- 1 tablespoon lemon zest
- 3 teaspoons lemon juice
- 1½ sheets leaf gelatin
- 2 tablespoons water, plus more for blooming the gelatin
- Special equipment: 4 or 5-inch ring to cut gelée
- Combine blueberries, half the sugar, half the lemon juice, and the lemon zest in a saucepan. Bring to simmer over medium heat, mashing berries slightly as you stir until berries burst
- Transfer the mixture to a food processor and puree until smooth.
- Measure out a ½ cup of the puree and place it back into the saucepan. Reserve the remaining puree for the blueberry lemon mousse.
- Bloom the gelatin by cutting the sheets into 1-inch strips and submerging them in cool water for 5-minutes to soften.
- Add remaining sugar and lemon juice to the saucepan with the puree. Heat until it begins to bubble.
- Wring out gelatin to remove excess water and add it to the warm blueberry sauce. Whisk to dissolve.
- Pour the mixture into an 8x8 inch pan lined with parchment paper. Refrigerate for at least 4-hours until set.
- When you are ready to assembler the cake, you will remove the gelée from the fridge and cut a 5-inch round out of the center.
- 2 large eggs, separated at room temperature
- ¼ cup granulated sugar, divided
- 1 tablespoon milk
- 1 tablespoon lemon zest
- 2 tablespoons lemon juice
- ¼ teaspoon vanilla extract
- ½ cup cake flour
- 14/ teaspoon sea salt
- Special equipment: 6-inch ring to cut the cake once baked
- Line an 8x8 inch pan with parchment paper and set aside. Preheat oven to 350 degrees Fahrenheit
- Beat the egg yolks in a bowl until light and creamy then whisk in 3 tablespoons of sugar. Whisk in milk, lemon juice, zest, and vanilla extract.
- Sift in the cake flour and salt. Fold until just incorporated.
- In a separate, clean bowl, whip egg whites until frothy and stiff peaks form. Beat in the remaining tablespoon of sugar.
- Gently fold the whites into the yolk-batter until fully combined.
- Pour batter into the prepared baking pan, spread it into a thin even layer, and bake 9-11 minutes until cake is spongey.
- Remove from the oven and let cool completely.
- When you are ready to assembler the cake, you will remove the gelée from the fridge and cut a 5-inch round out of the center.
- 3 sheets leaf gelatin
- ½ cup blueberry puree (leftover from making the gelée)
- ½ cup mascarpone cheese
- ¼ cup granulated sugar
- ¾ cup whipping cream
- ½ teaspoon vanilla extract
- 1 tablespoon lemon zest
- 2 tablespoons lemon juice
- pinch fine sea salt
- Special equipment: electric mixer
- Cut the gelatin into 1-inch strips and submerge in cool water to soften.
- Warm the ½ cup of blueberry puree until smooth and just bubbling. Wring on the gelatin to remove excess water and whisk the gelatin into the warm puree. Set aside to cool.
- In a medium bowl whisk together the mascarpone cheese, sugar, salt, zest, lemon juice, and vanilla extract. Add the cooled blueberry mixture and whisk until smooth.
- In a separate, clean bowl of a stand mixer, beat the heavy cream until it reaches stiff peaks. Add ½ of the blueberry mixture and fold to lighten the whipped cream then add the remaining cream and fold until fully incorporated.
- Immediately begin assembling your cake (see recipe titled Blueberry Lemon Mousse Cake Assembly
- 6 sheets leaf gelatin
- 1 cup of sugar
- ⅔ cup corn syrup or glucose syrup
- ½ cup water
- ½ cup sweetened condensed milk
- 7 ounces good-quality white chocolate, finely chopped
- Special equipment: immersion blender, optional
- Cut the gelatin into 1-inch strips and submerge in cool water to soften
- Place the white chocolate in a medium-size bowl and set aside
- Whisk together the sugar, corn syrup, and ½ cup water in a saucepan over medium-high heat and bring to a bowl until the sugar is dissolved. Remove from heat and add in the gelatin (writing out as much excess water as possible). Whisk in the sweetened condensed milk.
- Pour the hot mixture of the white chocolate and let it sit undisturbed for 30-seconds
- Stir the chocolate until it is completely melted, you may want to use an immersion blender here to expedite the process but be careful of forming air bubbles
- If you want to color your mirror glaze, separate it into bowls and add 2-3 drops of gel food coloring until the desired color is reached
- Allow the glaze to cool until it reaches 95-96 degrees. While the glaze cools, prep your frozen mousse cake for glazing following the instructions in the following recipe titled Blueberry Lemon Mousse Cake Assembly
- 5-inch blueberry gelée
- 6-inch lemon sponge
- prepared blueberry-lemon mousse
- mirror glaze (prepared at step 7 which is the next day after freezing the mousse cake)
- Special equipment: quarter sheet pan, 6-inch cardboard cake round, 6-inch cake ring, acetate strips at least 6-inches tall and long enough to line the inside of the 6-inch cake ring, piping bag, parchment paper
- Line a quarter sheet pan with parchment paper
- Place a 6-inch cake ring on top of the parchment and line the inside of the ring with acetate so
- Place the 6-inch cake board into the cake ring and then place the 6-inch round lemon sponge onto the cake board inside the cake ring
- Place the 5-inch blueberry gelée on top of the sponge
- Put the blueberry-lemon mousse into the piping bag and pipe the mousse on top of the sponge & gelée
- Place the entire thing into the freezer and allow it to freeze overnight. Be sure to place the cake into the freezer on a level surface so the cake freezes flat
- The next day, make the mirror glaze then remove the frozen cake from the freezer
- Gently remove the ring and acetate from the cake, you may need to warm the sides a bit so it slips off
- Place the cake onto a small bowl turned upside down so the cake edges hang cleanly over the bowl, this will allow your mirror glaze to cleanly drip off the edges of your cake.
- Place the bowl & cake onto a sheet pan to catch the mirror glaze as it drips off
- Once your mirror glaze has cooled to 95 degrees Fahrenheit, pour your glaze of the cake starting and the center and alternating colors (if you colored your mirror glaze). Continue to pour the mirror glaze until the top and all sides of the cake are encased in the glaze. Allow excess glaze to drip off for 5-minutes then use a clean, offset spatula to clean up the edges of the cake.
- Place the cake on your cake stand or serving plate and place the cake in the fridge for at least 4-hours before serving.
- The cake can be kept in the fridge for up to 3-days after fully assembled.
For my blueberry pie crust, I used 
