Preheat oven to 350°F. Grease a square nonstick metal baking pan (9-or 10-inch works best here) and set aside.

In a large microwave-safe bowl, add 1 cup of the chocolate chips, the chopped dark chocolate, and the cubed butter. Heat in 30-second increments, stirring in between each, until fully melted and smooth, about 2 minutes total. Set aside.

In a medium bowl, sift together the flour, cocoa powder, baking powder, and salt. Add espresso granules and stir to combine.

In another large bowl, add granulated sugar, eggs, vanilla extract, and coffee liqueur (if using). Beat with an electric mixer on medium-high speed until light-colored, about 2 minutes.

Add the melted chocolate to the sugar mixture and beat until well combined. Add ½ of the flour mixture and beat at low speed until combined. Add the remaining flour mixture and continue to beat until well blended. Stir in the remaining ½ cup of chocolate chips.

Pour the mixture into the prepared baking pan and bake for 30-35 minutes or until a cake tester or  toothpick inserted 2 inches from the side comes out clean.

Cool completely, then run a butter knife around the edge of the pan to help them come out easily. Transfer to a cutting board and cut into triangles to serve, dusting with powdered sugar if desired.