Preheat your oven to 350°F (175°C). Grease an 8x8 inch baking pan and line it with parchment paper, leaving an overhang on the sides to easily lift the brownies out later.

In a medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking soda, and salt. Set it aside.

In a large bowl, whisk together the melted butter and granulated sugar until well combined. Add the eggs and extra egg yolk one at a time, whisking well after each addition. Stir in the buttermilk, white vinegar, vanilla extract, and red food coloring until the batter is uniformly vibrant red.

Gently fold the dry ingredients into the wet ingredients using a spatula. Mix only until you no longer see streaks of flour—do not overmix!

Pour the batter into your prepared pan and spread it into an even layer. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached, but not wet batter.

Let the brownies cool in the pan on a wire rack completely before frosting. This is crucial for the frosting to set properly.

In a large bowl, use an electric mixer to beat the softened cream cheese and butter on medium speed until smooth and creamy.

Reduce the speed to low and gradually add the powdered sugar, mixing until just combined. Add the vanilla extract, then increase the speed to medium-high and beat for 2-3 minutes until the frosting is light and fluffy.

Once the brownies are completely cool, spread the frosting evenly over the top. You can make decorative swirls with the back of a spoon.

For the cleanest slices, chill the brownies in the refrigerator for at least 30 minutes before cutting.