Sift together cake four, baking powder, and salt. Whisk together buttermilk and egg whites.
Put the sugar and lemon zest in the bowl of the mixer and rub it together with your fingers. Dorie says to do this, so I do. Add the butter and cream together until creamy, 3 minutes. Add the lemon extract. Add ⅓ of the flour mixture. Add ½ of the buttermilk mixture. Repeat until all of the ingredients are added. Add the sprinkles and fold until combined.
Pour batter into 8 or 9-inch pans that have been sprayed with cooking spray with flour. Bake at 350 degree for 30 to 35 minutes. Cool in pans for 10 minutes, then turn out and cool completely.
Ice with frosting. I used my Marshmallow Buttercream with lemon extract instead of vanilla bean.