Meanwhile, in medium bowl, beat icing sugar, 1/4 cup softened butter, 2 to 4 tablespoons milk and 1/2 teaspoon vanilla with spoon until smooth and fluffy. If frosting is too stiff to spread, add additional milk, 1 teaspoon at a time. Tint with food colour. Using knife, spread slightly less than 1 teaspoon frosting on each cooled cookie; top with sprinkles. Store covered in airtight container at room temperature.