Get Ready: Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper and give it a light grease. Set it aside.
Melt It Down: In a large, microwave-safe bowl, combine the butter and ½ cup of the chocolate chips. Microwave in short 30-second bursts, stirring in between, until everything is smooth and melted (this usually takes about 1-2 minutes).
Mix in Dry: Stir in the cocoa powder, salt, and optional espresso powder until well combined.
Add Sugars: Mix in both the white granulated sugar and the brown sugar until fully incorporated.
Whisk in Wet: Whisk in the eggs, one at a time, followed by the peppermint extract and vegetable oil, until the mixture is smooth.
Fold in Flour & Chips: Gently fold in the flour and the remaining chocolate chips just until no dry streaks of flour remain. Be careful not to overmix!
Bake: Pour the brownie batter into your prepared pan and spread it evenly. Bake for about 35-40 minutes. The brownies are ready when a toothpick inserted into the center comes out with a few moist crumbs, but not wet batter. This keeps them fudgy! Let them cool completely in the pan.
Make Ganache: While the brownies cool, prepare the ganache. Place 1 cup of chocolate chips in a medium heat-proof bowl. In a small saucepan, warm the heavy cream over medium heat until it's just warm and steaming, but not boiling.
Combine Ganache: Pour the warm cream over the chocolate chips and let it sit for 3-4 minutes to melt the chocolate. Then, whisk until it's smooth and creamy. Stir in the peppermint extract, 1 teaspoon of butter, and a pinch of salt.
Finish & Chill: Spread the smooth ganache evenly over the cooled brownies. Sprinkle with crushed peppermint candies for a festive touch. Pop the brownies into the fridge for at least an hour to let the ganache set. Once firm, cut into squares with a sharp, clean knife and enjoy your delightful, healthy-ish holiday treat!