Preheat oven to 350 degrees and lightly grease a baking sheet.

In a large bowl, beat butter and sugar for about 2 minutes or until creamy. Stir in egg, food coloring and vanilla until completely blended. Mix in flour, cocoa and salt until blended.

Roll dough into 1-inch balls. Place balls 2 inches apart on your prepared baking sheet. Press thumb into center of each cookie to make indentation, but be careful not to press all the way to the cookie sheet.

Bake for 10-12 minutes. Allow to cool on cooling racks.

To make the frosting, beat together the butter and cream cheese until light and fluffy (1-2 minutes). Mix in vanilla. Gradually mix in powdered sugar until incorporated. Pipe into the center of each filled cookie. Add sprinkles if desired. Store in airtight container at room temperature or chilled.