2 sticks (1 cup) unsalted butter
2/3 cup unbleached all-purpose flour
2 cups granulated sugar
4 large eggs (room temperature)
1 teaspoon pure vanilla extract
1 teaspoon prepared strong coffee
1 tablespoon liqueur, such as Frangelico or Grand Marnier (optional)
3/4 cup unsweetened natural cocoa powder (not Dutch process)
1/2 teaspoon baking powder
1/2 teaspoon fine sea salt
Preheat oven to 350*F with rack in middle of oven. Spray an 8x8 or 9x9 inch metal baking pan with cooking spray, then line with criss-crossing sheets of parchment, spraying between the layers and on the top layer, leaving an overhang to make easy removal from pan.
Melt butter in a medium saucepan. Remove from heat and stir in sugar with a spatula. Add eggs, vanilla, coffee, and liqueur, if using, and mix until blended. Stir in dry ingredients, slowly at first, then more quickly as the mixture blends, until batter is smooth.
Spread batter in pan and bake 32-40 minutes (lower end of time scale for an 8x8 pan, upper end for a 9x9 pan), or until an inserted toothpick comes out with a few moist crumbs holding on. Cool completely on a wire rack.
Cut into 16 squares. Store tightly wrapped at room temperature.
Recipe adapted from finecooking.com