Preheat your oven to 350°F (175°C) and grease a mini muffin pan with butter or cooking spray.

In a medium mixing bowl, sift together the cocoa powder, all-purpose flour, salt, and espresso powder.

In a saucepan over low heat, melt the butter until completely liquid, then mix in the sugar, vanilla, red food coloring, and vinegar until smooth.

Let the melted mixture cool for a few minutes, then whisk in the eggs, one at a time.

Carefully fold the dry ingredient mixture into the wet batter using a spatula.

In a separate bowl, beat the cream cheese with sugar and vanilla extract until smooth.

Fold in the egg yolk into the cream cheese mixture until well combined.

Spoon approximately 1 tablespoon of brownie batter into each muffin cup, followed by 1 teaspoon of the cream cheese mixture, and top with another teaspoon of brownie batter.

Using a toothpick or a small skewer, gently swirl the brownie batter and cream cheese filling together.

Place the muffin pan in the preheated oven and bake for approximately 12 minutes.

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

Once fully cooled, store your Red Velvet Brownie Bites in an airtight container in the fridge for up to 5 days.