Preheat your oven to 350°F (175°C). Grease an 8-inch square baking pan with non-stick spray or line it with parchment paper, then lightly spray the paper.

In a microwave-safe bowl, melt the stick of butter in the microwave. Let it cool slightly, then pour it into a large mixing bowl.

To the bowl with the melted butter, add the granulated sugar, eggs, and vanilla extract. Stir until the mixture is smooth and well-combined.

Gradually sift in the flour, cocoa powder, baking powder, and salt. Mix just until the batter is smooth and no streaks of flour remain.

Pour the batter into the prepared pan and spread it evenly. Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.

Let the brownies cool completely in the pan on a wire rack before you start the frosting.

For the frosting, dissolve the instant coffee granules in the heavy whipping cream, stirring until fully dissolved. Set aside.

In a separate bowl, beat the softened butter with an electric mixer until light and fluffy. Gradually add the powdered sugar, beating on low speed until combined.

Slowly pour in 2 tablespoons of the coffee-cream mixture and beat on medium speed until smooth. If the frosting is too thick, add more cream, 1 tablespoon at a time, until you reach a spreadable consistency.

Once the brownies are completely cool, spread the coffee frosting evenly over the top. Slice into squares and serve.