Preheat the oven to 350°F. Grease and flour a 9 x 13 baking pan.

In a bowl, mix together the flour, cocoa powder, salt, and baking powder. Set aside.

In a mixer beat the butter and sugar together until light and fluffy.

Beat in the eggs until fully combined.

In a separate bowl, mix together the buttermilk, sour cream, vinegar, baking soda, vanilla, and food coloring.

Alternate between adding the flour mixture in three additions and the buttermilk mixture in two additions to the butter mixer. Mix each addition of flour and buttermilk well before adding the next.

Pour the mixture into the prepared baking pan.

Bake for 30 - 35 mins, or until a toothpick comes out with a few crumbs clinging to it.

Allow to cool completely.

Make the frosting while the cake cools.

Beat the butter and cream cheese together until smooth.

Beat in the powdered sugar one cup at a time until fully incorporated. The mixture may seem crumbly, that is normal.

Drizzle in the heavy cream one tablespoon at a time until the mixture is your preferred texture.

Mix in the salt and vanilla and mix well.

Slather the top of your red velvet sheet cake with the frosting and serve.