Preheat your oven to 350°F (175°C) and grease a mini muffin pan.

In a medium bowl, sift in the cocoa powder to remove any lumps.

Melt the butter in a saucepan over low heat, then stir in the sugar, sifted cocoa, vanilla extract, red food coloring, salt, espresso powder, and vinegar until smooth. Let this mixture cool slightly.

Whisk in the eggs one at a time until fully incorporated.

Gently fold in the flour using a spatula until just combined.

In another bowl, beat the cream cheese with sugar and vanilla extract until smooth. Incorporate the egg yolk.

Spoon the brownie batter into the prepared muffin cups, filling them halfway. Add a dollop of the cream cheese mixture on top and swirl with a toothpick.

Bake for about 12 minutes until edges are set and centers look slightly soft.

Let the brownie bites cool in the pan for 5 minutes before transferring to a wire rack.