adapted from Fine Cooking
1 cup unsalted butter
2 cups granulated sugar
4 large eggs (room temperature)
1 teaspoon pure vanilla extract
1 teaspoon prepared strong coffee
3/4 cup unsweetened natural cocoa powder (not Dutch process)
2/3 cup unbleached all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon fine sea salt
Preheat oven to 350F with rack in middle of oven. Spray an 8×8 or 9×9 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 using a spatula. Add eggs, vanilla, and coffee, mix until blended.
Stir dry ingredients together.
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 8×8 pan, upper end for a 9×9 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.