I know, I know, I know... it looks like my 2-year-old decorated these... they could have been way cuter if I had any patience at all!
1/2 cup (1 stick unsalted butter, plus more for baking pan
1 cup all-purpose flour
1/3 cup unsweetened cocoa powder
1/2 teaspoon baking powder
1/2 teaspoon salt
1 and 1/4 cups sugar
1/2 pound bittersweet chocolate chips (1 and 1/2 cups)
3 large eggs
1 teaspoon pure vanilla extract
32 miniature York peppermint patties
York pieces (white ones only) for eyes
chocolate chips and icing pens, for decorating
Preheat oven to 350 degrees. Lightly butter an 8-inch square metal baking pan and line with parchment paper, leaving a 2-inch overhang on all sides.
In a large bowl, whisk together flour, cocoa powder, baking powder, and salt.
In a medium saucepan, melt butter, sugar, and bittersweet chocolate over medium, stirring frequently, until smooth. Add to flour mixture and stir to combine. Stir in eggs and vanilla, then let cool to room temperature, 10 minutes.
Transfer batter to pan. Press 16 peppermint patties evenly into batter and, with a small offset spatula, evenly spread batter to completely cover patties.
Bake until cake is puffed and just set, about 35 minutes. Let cool on a wire rack, 25 minutes, then top with 16 peppermint patties. Let cool 25 minutes more, then decorate with York pieces dotted with chocolate for eyes and chocolate chips for ears. Refrigerate until chocolate is set, 5 minutes. Decorate with icing pens. Using parchment, lift cake from pan and cut into 16 squares.