Preheat the Oven: Set your oven to 350°F (175°C) and grease a small baking dish.
Melt Butter and Chocolate Chips: In a microwave-safe bowl, melt the butter and chocolate chips together in 15-second increments, stirring in between, until smooth.
Mix in Sugars: Add the brown sugar and white sugar to the melted mixture and stir to combine.
Incorporate Egg and Vanilla: Add the egg yolk and vanilla extract, mixing until well incorporated.
Combine Dry Ingredients: Sift in the cocoa powder, flour, and salt, folding gently until just combined.
Bake: Pour the batter into the prepared dish and bake for 18-22 minutes. The edges should be set, but the center will be slightly soft.
Serve: Let the brownie cool for 5 minutes, and then add a large scoop of ice cream on top before serving.
Notes
Make sure to dissolve sugars into your warm melted butter and chocolate chip mixture! Otherwise your brookie will be gritty.