Cream 2 sticks of butter and both sugars til fluffy. Add eggs and vanilla.
In a separate bowl, whisk flour, baking powder and salt.
Slowly stir in the dry ingredients into the butter mixture until well blended.
Chill dough for 30 minutes.
Roll into balls and flatten.
Bake at 350 for 15-17 minutes.
Mix all ingredients together with a wooden spoon until thick and smooth.
Add more water if icing is too thick.