Preheat oven to 350°F and prepare an 8-inch square baking pan with non-stick spray. Line with parchment paper if desired for easy removal.

Melt 1 stick butter in a microwave-safe bowl in 30-second intervals. Let cool for 1-2 minutes until warm but not hot.

Combine melted butter, 1 cup sugar, 2 eggs, and 1 teaspoon vanilla in a large bowl. Stir until smooth and well combined, about 1-2 minutes.

Add 2 teaspoons coffee extract (or 1 tablespoon instant coffee) to the wet mixture and stir to incorporate.

Add 1/3 cup cocoa powder, 1/2 cup flour, 1/4 teaspoon salt, and 1/4 teaspoon baking powder all at once. Mix just until no flour streaks remain. Do not overmix.

Pour batter into prepared pan and spread evenly with a spatula. The batter will be thick.

Bake for 30-35 minutes until edges are set and a toothpick inserted in center comes out with a few moist crumbs. Cool completely in pan.

For frosting: Mix 1 1/2 teaspoons instant coffee with 2 tablespoons heavy cream until mostly dissolved. Set aside.

Beat 1/3 cup softened butter with electric mixer until light and fluffy, about 2 minutes on medium speed.

Gradually add 2 cups powdered sugar, about 1/2 cup at a time, beating well after each addition.

Pour in coffee-cream mixture and beat on medium-high until smooth and spreadable. Add more cream 1 tablespoon at a time if too thick.

Spread frosting over cooled brownies using an offset spatula. Let set for 15 minutes before cutting into 16 squares.