This seems to be the most requested cookie in my arsenal. I have to admit, it's one of my favorites as well. As this is my signature sweet, I can't give away my tricks. But here's the basic recipe:
1 cup butter (softened)
1/2 cup powdered sugar
2 c flour
Preheat oven to 350 degrees. Cream together butter and powdered sugar. Add flour half cup at a time until dough is smooth. Form dough into balls about 3/4" in diameter. Using your thumb, make a well into the dough. Bake cookies 10-12 minutes or until bottoms begin to brown. Cool completely and fill wells with icing.
Melt 1/2 stick butter with 1/4 cup milk or half and half. Beat in powdered sugar until proper consistency. Add 1 tsp. vanilla and food coloring if desired. *OPTIONAL: add a few drops of mint, orange, cherry, or any other flavoring in place of vanilla*