Stir together sugar and butter until smooth. Add vanilla and eggs, and beat well.
Stir the baking powder into the flour, and the baking soda into the buttermilk.
Add the flour mixture and the buttermilk mixture alternately to the sugar/butter in a large mixing bowl, beginning and ending with the flour.
Stir dough til smooth. Store tightly covered in the refrigerator, for several hours or overnight.
Preheat oven to 375 degrees F.
Drop cookie dough in large spoonfuls onto an ungreased cookie sheet, leaving plenty of room between they do expand.
Bake 10 minutes at 375, until light brown in color.
While hot, use a spatula to loosen the cookie sheet, and put it on a rack to cool.
Frosting:
½ cup butter
1 cup packed brown sugar
¼ cup milk
Pinch of salt
1 tsp vanilla
2 cups powdered sugar
Melt the butter in a saucepan. Stir in brown sugar, until smooth and dissolved.
Remove the pan from heat, and add milk, salt, and vanilla.
Set aside and cool to lukewarm. Gradually mix in powdered sugar until desired consistency. Spoon icing over cooled cookies.
Delicious!