Preheat oven to 350°F and prepare a 9×13-inch pan by greasing and lightly flouring it or spraying with baking spray.

In a large mixing bowl, cream the softened butter with sugar using a hand or stand mixer until pale and fluffy, approximately 2–3 minutes. Blend in the red food coloring and vanilla extract until fully incorporated.

Add the eggs individually, mixing after each until just combined.

In a separate bowl, whisk together flour, cocoa powder, salt, and baking soda. Gradually mix the dry ingredients into the butter mixture, alternating with buttermilk and vinegar, combining gently with a wooden spoon until just mixed; do not overwork the batter.

Pour the mixture evenly into the prepared pan and bake for 25–30 minutes, or until a toothpick inserted into the center emerges clean.

Remove from oven and, while still warm, pierce the cake with a fork. Pour the condensed milk over the surface, allowing it to seep into the holes. Let the cake cool completely before frosting.

To prepare the frosting, whip together butter and cream cheese on high speed for 2–3 minutes. Lower the speed and gradually mix in the powdered sugar, followed by salt, vanilla extract, and milk. Continue to beat until the frosting is smooth and fluffy, about 2–3 minutes more.

Evenly spread the frosting over the cooled cake and garnish as desired.