Preheat your oven to 350°F (175°C) and prepare an 8-inch baking dish by greasing it or lining it with parchment paper.

Melt unsalted butter in a microwave-safe bowl until fully liquefied, then cool slightly before mixing with other ingredients.

Stir in granulated sugar, followed by eggs and vanilla extract into the melted butter and mix until smooth and glossy.

In a separate bowl, whisk together flour, cocoa powder, baking powder, and salt. Gradually add dry ingredients to the wet mixture, stirring until combined.

Spread the brownie batter into the prepared dish and bake for 30-35 minutes until a toothpick comes out clean.

Let brownies cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

Dissolve instant coffee granules in heavy whipping cream in a small bowl and set aside.

Beat unsalted butter until light and fluffy, then incorporate powdered sugar until pale and airy.

Gradually mix in the coffee-infused cream until the frosting is smooth and spreadable.

Spread the frosting over completely cooled brownies, slice into squares, and serve.