Preheat your oven to 350°F (175°C) and prepare an 8"x8" metal baking pan with parchment paper.

Melt the butter and semi-sweet chocolate in a microwave-safe bowl, heating in 30-second intervals.

Incorporate granulated sugar and light brown sugar into the melted mixture, whisking until incorporated.

Whisk in the vanilla extract and eggs one at a time until the mixture is glossy.

Gently fold in flour, cocoa powder, espresso powder, and salt until just combined.

Spread the batter into the prepared pan and bake for 30 to 35 minutes.

Allow cooling completely in the pan on a wire rack.

Heat the heavy cream until simmering and pour it over the chopped chocolate; let sit for 2 minutes, then stir until smooth.

Cool the ganache to room temperature, then whip until light and fluffy.

Pipe the whipped ganache onto the cooled brownie bites.