Preheat your oven to 350ºF (about 175ºC). This is an essential step to ensure that your brownies bake evenly. While the oven is warming, line an 8 x 8-inch baking pan with non-stick foil or regular foil sprayed with non-stick cooking spray to prevent sticking.
In a large, microwave-safe bowl, melt butter using 30-second increments. Stir in between to avoid overheating. You want it just melted, not boiling. This step is crucial for the perfect brownie texture.
Add the granulated sugar and brown sugar to the melted butter, mixing until combined. The mixture should be smooth and glossy.
Next, add in the eggs, coffee, and vanilla, stirring until well mixed. This is where the magic happens, as the sugars dissolve and blend with the other ingredients.
Now it’s time to add the cocoa powder and the espresso mixture. Whisk until everything is smooth—this is the base of your brownies and should be rich and dark.
Gently fold in the flour, cornstarch, and baking powder. Make sure not to overmix; you want to keep that fudgy texture we all love. Stir until just combined, with no visible flour remaining.
Pour the batter into the prepared pan, smoothing the top lightly with an offset spatula. It should look even and inviting as it's ready to go into the oven.
Bake for about 28 to 30 minutes. You'll know they’re done when the top looks set and a toothpick inserted into the center comes out clean or with a few crumbs. It’s okay to have a little bit of fudginess!
Once done, remove the brownies from the oven and let them cool in the pan on a wire rack. Cooling is essential to achieve the right texture.
Meanwhile, prepare the ganache. In a medium, microwave-safe bowl, combine chocolate chips and heavy cream. Microwave on high for one minute. Let it sit for a few minutes.
After letting it stand, whisk the mixture to combine. If there are small lumps, microwave for an additional 15 seconds and whisk until smooth. Be patient; the ganache will come together!
Pour the ganache over the cooled brownies, smoothing it out with an offset spatula. Sprinkle with colorful sprinkles or candies for that extra touch.
Chill the brownies in the refrigerator for at least 2 hours before cutting. This helps the ganache set nicely and makes cutting easier.