Cream the butter, add sugar, and egg well beaten. Mix and sift baking powder, salt, and flour; add to first mixture; then add milk, peanuts, and lemon juice. Drop from a teaspoon on a buttered sheet one inch apart, and place one-half peanut on top of each. Bake twelve to fifteen minutes in a slow oven. This recipe will make twenty-four cookies. One pint peanuts when shelled should yield one-half cup.