Preheat oven to 350 F degrees (175 C degrees ) and place rack in center of oven. Line and grease sides of two 8" or 9" pan.
In a mixing bowl sift together the flour, salt, and cocoa powder. Set aside.
In bowl of your electric mixer, or with a hand mixer, beat the butter until soft (about 1-2 minutes). Add the sugar and beat until light and fluffy (about 2-3 minutes). Add the egg, beating well. Scrape down the sides of the bowl. Add the vanilla extract and beat until combined.
In a measuring cup whisk the buttermilk with the red food coloring. With the mixer on low speed, alternately add the flour mixture and buttermilk to the butter mixture, in three additions, beginning and ending with the flour.
In a small cup combine the vinegar and baking soda. Allow the mixture to fizz and then quickly fold into the cake batter.
Pour batter into prepared pans. Bake in the preheated oven for approximately 30 minutes, or until a toothpick inserted in the center of the cakes comes out clean. Let cupcakes cool for about 5 minutes in the pan before inverting them in a wire rack to cool completely.
Make the Cream Cheese Frosting: Beat cream cheese and butter until free of lumps, add sifted confectioner's sugar and beat until smooth, add double cream or all-purpose cream and vanilla extract; continue beating until smooth and creamy.