Preheat the oven to 350°F. Grease a 9″ x 13″ pan and set aside.
In a large saucepan, melt the butter over low heat. Add the sugar and stir to combine. Return the mixture to the heat, just until it’s hot, but not bubbling. It will become shiny as you stir. Remove from heat and stir in the cocoa, baking powder, salt, and vanilla extract.
Add the eggs, stirring until smooth. Add the flour and stir until just combined.
Spoon half of the batter into prepared pan. Place the peppermint patties on top of the batter. Pour the remaining batter over the peppermint patties and gently smooth. Tap the pan on the counter to even the batter out.
Bake the brownies for 35 minutes, until a toothpick inserted into the center comes out clean, or with just a few moist crumbs clinging to it. The brownies should feel set on the edges, and the center should look very moist, but not uncooked. Remove them from the oven and cool completely.
To make the ganache, add the chocolate to a large bowl. Heat the cream in a small saucepan over medium heat just until it bubbles around the edges. Remove the cream from the heat and pour it over the chocolate. Let the mixture stand for 30 seconds, then stir until the chocolate melts and a smooth ganache comes together, about 1-2 minutes. Pour it over the top of the brownies, then cover with the chopped peppermint patties. Let the brownies sit for 30 minutes before cutting. Cut, serve, and enjoy!