Preheat your oven to 350°F and generously grease a mini muffin pan with butter or cooking spray, making sure to coat the sides and bottoms of each cup. This prevents sticking and ensures clean release. Sift the cocoa powder into a small bowl to remove any lumps—this prevents streaks in your final brownies. Have all ingredients at room temperature, especially the cream cheese (around 70°F) and eggs, as this helps them blend smoothly and incorporate air for better texture.

In a medium bowl, melt the 9 tablespoons of butter and whisk together with the 1 1/4 cups sugar, sifted cocoa powder, 1/2 teaspoon vanilla, red food coloring, 1/8 teaspoon salt, espresso powder, and vinegar. The espresso powder enhances the chocolate flavor without making it taste like coffee, while the vinegar adds tang that deepens the red velvet character. Once combined, whisk in the 2 eggs one at a time, ensuring each is fully incorporated. Finally, gently fold in the 3/4 cup flour until just combined—overmixing develops gluten and makes brownies tough, so stop as soon as you see no dry flour streaks.

In a separate bowl, beat the room-temperature cream cheese with 3 tablespoons sugar and 1/2 teaspoon vanilla until smooth and creamy—about 1 minute of mixing. I like to use a whisk to avoid overbeating, which can make the filling grainy. Gently fold in the egg yolk until just combined. This filling will stay soft during baking and create a luxurious contrast to the fudgy brownie.

Working with the greased mini muffin pan, spoon about 1 tablespoon of brownie batter from Step 2 into each cup, filling it roughly halfway. Top each with about 1 teaspoon of the cream cheese filling from Step 3, then add another 1 teaspoon of brownie batter on top to seal it. Using a toothpick or thin skewer, drag it through the layers in a figure-eight or circular motion to create a swirled pattern—don't overmix or you'll muddy the red velvet effect. The key is gentle swirling just enough to create visual interest without fully blending the layers.

Bake the pan in your preheated 350°F oven for 12 minutes—the tops should look just set and spring back lightly when touched, but the centers will still be slightly soft and fudgy. Remove from the oven and let the bites cool in the pan for 5 minutes, which helps them set enough to remove cleanly without crumbling. I recommend using a thin knife or small offset spatula to gently pop each bite from the pan once they've cooled slightly—this prevents them from breaking apart. Allow them to cool completely on a wire rack before serving.