(the original recipe has been passed down through my family, but came-i think-from Paula Peck)
1 cup butter-room temperature
3/4 cup sifted powdered sugar
1 tsp vanilla extract
1/2 tsp salt
2 cups flour
Beat sugar and butter until completely mixed together, but not light and fluffy. Add vanilla and salt and mix until just incorporated. Slowly stir in flour and only mix until just incorporated. Divide dough in 2 portions, wrap in plastic and place in refrigerator for a few hours or overnight. When ready to bake, roll out and bake on parchment paper. top with sprinkles or leave plain and bake at 325 until just starting to brown on the bottom.
once cooled you can dip in tempered chocolate or glaze with royal icing (alton brown recipe here), flavored as you choose