Preheat your oven to 350°F (175°C).
In a large bowl, cream together the softened butter and granulated sugar.
Add the egg, red food coloring, and vanilla extract to the mixture.
In another bowl, combine the flour, baking soda, cocoa powder, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk.
Scoop tablespoon-sized portions of dough onto a lined baking sheet.
Bake for 10-12 minutes, until edges look firm but centers are slightly soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.
While cookies cool, prepare the cream cheese frosting by beating the cream cheese, powdered sugar, and milk until smooth.
Frost the cooled cookies and serve immediately, or store in a cool place.