Preheat the oven to 350ºF.
In a large bowl, whisk together the eggs, baking cocoa, salt, baking powder, espresso mixed with water, and vanilla until well combined.
Stir in the sugar and melted butter until well combined, then stir in the flour. (A firm rubber spatula works best.) Set brownie batter aside.
In a separate bowl, prepare the cheesecake filling by stirring together the cream cheese, sugar and egg yolk until well combined. Transfer the mixture to a pastry bag or plastic bag.
Grease a non-stick mini-muffin pan with cooking spray or butter and then spoon a tablespoon of brownie batter into the greased cups.
Pipe a generous amount of cheesecake filling atop the brownie batter.
then top off each cup with an additional teaspoon of brownie batter.
Bake for about 12 minutes, or until a toothpick inserted comes out clean.
Let the brownie bites cool for 10 minutes in the pan and then transfer them to a cooling rack to continue cooling, or enjoy warm.
When measuring flour, never scoop the cup into the flour, as it condenses the flour and causes you to use more than the recipe intends. Instead, spoon the flour into your measuring cup and level it with a knife. The same technique applies for cocoa powder.
A mini-ice cream scoop is an easy and efficient way to scoop the brownie batter into the prepared cups.
Feel free to swirl the cheesecake mixture with the brownie mixture once scooped into the muffin cups to create a marbled effect.
If the brownie bites aren't easily releasing from the pan, use a sharp knife to cut around the edges to release them.