1. Preheat oven to 350°F (175°C). Grease or line an 8×8-inch baking pan with parchment paper.

2. Melt butter in a medium saucepan over low heat. Remove from heat and stir in sugar until glossy.

3. Add eggs one at a time, whisking well after each addition. Stir in vanilla extract.

4. Sift in cocoa powder, flour, salt, and baking powder. Mix gently until combined — do not overmix.

5. (Optional) Stir in espresso powder for a mocha flavor boost.

6. Pour batter into the prepared pan and spread evenly.

7. Bake for 30–35 minutes, or until edges are set and a toothpick inserted in the center comes out with moist crumbs.

8. Cool completely on a wire rack before frosting.

For the Coffee Frosting:

1. Dissolve instant coffee granules in warm cream or milk. Set aside.

2. Beat butter until creamy and pale. Gradually add powdered sugar, then pour in the coffee mixture and a pinch of salt.

3. Whip until light, smooth, and spreadable. Adjust consistency with more cream if needed.

4. Frost cooled brownies and create soft swirls with the back of a spoon.