Line a 9x13 inch pan with a sheet of parchment paper
In a medium-sized bowl, sift together the flour, cocoa, baking soda, baking powder, and salt. Set aside
In the bowl of a stand mixer with a paddle attachment, beat the softened butter on medium until creamy, 1-2 minutes
Add in both the sugars and mix another minute on medium
Add the egg, vanilla, and yogurt, beating until combined
Add in the flour-cocoa mixture in 2 additions until all the dry ingredients are fully combined*
Turn the dough out into the prepared pan and using your hands or a small rolling pin, evenly spread the dough into all corners of the pan
Place in oven and bake for 13-14 minutes
Allow the cookies to cool completely before frosting.
To make the frosting combine 2 cups vanilla frosting with ¼ teaspoon of peppermint extract, adding more as desired
Frost the cookies using an offset spatula and cut into bars, remove cookies from pan & decorate
To decorate, use the black frosting and a Wilton 2 tip to draw lines on to the cut bar cookies
Adorn the cookies with mini M&Ms set on their side to look like holiday string lights
Notes
* You may need to use our hands to fully incorporate the dry mixtures as the electric mixer often leaves flour at the bottom of the bowl ** Alternately, you can color a ½ cup of the remaining vanilla frosting black and place it in a decorator's bag with a Wilton 2 tip rather than purchasing pre-made black frosting
Recipe by Her Modern Kitchen at https://www.hermodernkitchen.com/peppermint-chocolate-cookie-bars/