1. Preheat the oven to 325°F. Butter an 8-inch square baking pan, line with parchment paper or foil, and butter the parchment. 2. In a large saucepan, heat the butter and bourbon over medium heat, stirring occasionally, until the butter melts. Stir in the cocoa powder until smooth. Remove from the heat and immediately add 1½ cups chocolate chips. Stir until smooth. Let cool slightly. 3. Add the eggs, one at a time, beating well after each addition. Stir in the confectioners' sugar until well-combined. Transfer to the prepared pan and spread in an even layer. Sprinkle the remaining ½ cup chocolate chips on top. 4. Bake until the top is glossy and a toothpick inserted 1 inch from the edge comes out clean, about 20 minutes. Cool completely in the pan on a wire rack. 5. Lift out of the pan using the parchment paper. Cut into 12 bars.