1/2 cup unsalted butter
1/4 cup unsweetened cocoa
3/4 cup lightly packed premium unsweetened natural cocoa
1-1/2 tablespoons canola oil
1/2 cup water
1 cup all-purpose flour
1 cup sugar
1/2 teaspoon baking soda
1/4 teaspoon fine sea salt
1/4 cup buttermilk (or soured milk – add a splash of vinegar to milk and let it sit for 10 minutes)
1 teaspoon vanilla
1 sleeve Girl Scout cookies, chopped (I used Do-Si-Dos)
1/4 cup unsalted butter
1/8 cup unsweetened cocoa
1 teaspoon vanilla
3 tablespoons milk
1-1/2 cups powdered sugar
1 cookie for garnish
1. Preheat your oven to 375 degrees F. Grease a 9-inch round cake pan.
2. Melt 1/2 cup the butter in a medium-sized saucepan over medium heat. Whisk in the cocoa (1/4 cup). Add the oil and water and bring to a rolling boil for 30 seconds.
3. Remove the pan from the heat and set it aside to cool slightly.
4. Whisk together flour, sugar, baking soda, and salt in a large bowl.
5. Pour the warm cocoa mixture into the dry ingredients and whisk until just combined.
6. In a separate bowl, whisk together the buttermilk (or soured milk), egg, and vanilla.
7. With a rubber spatula, stir the buttermilk mixture into the batter.
8. Spread chopped cookies evenly in the bottom of your prepared pan. Pour the batter over the top and place in the center of the oven. Bake until the top is firm and the cake starts to pull away from the sides of the pan – about 30 minutes.
9. Let the cake cool in the pan for 10 minutes, then turn out onto a cooling rack to finish cooling.
Make the frosting
1. Melt the butter in a saucepan over medium heat. Whisk in the cocoa and bring the mixture to a rolling boil; boil for 30 seconds.
2. Remove from heat and whisk in the milk and vanilla.
3. Add the confectioners’ sugar 1/2 cup at a time while whisking continuously.
4. Immediately pour the frosting over the cake (the cake should be bottom-side, i.e. flat-side, up), spreading with a spatula. The frosting will harden pretty quickly. Sprinkle an extra crumbled cookie on top.