In large bowl, cream together butter and sugar for 4 minutes.
Add eggs, vanilla, and red food coloring and mix until combined.
Add cocoa, flour, baking soda, and salt and stir together.
Lightly spray a 9 x 13 pan with non-stick cooking spray and spread batter evenly in pan.
Bake for 18 - 22 minutes, or until toothpick or cake tester comes out clean. Cool.
Frosting:
In large bowl, cream together butter and cream cheese until light and fluffy. Add powdered sugar and stir until combined. Add optional vanilla and salt. Chill for 5 minutes.
Spread onto cooled red velvet cookie bars. Garnish with sparkling sugar, white sprinkles, or M & M's. Cut into squares