This is a copycat recipe from another one I saw on here-- but not a duplicate, because this is intended to be made for frosting than for bonbons (though it certainly could be used that way.) By "extract", vanilla extract is the most commonly used one for traditional buttercream flavor. But this is a versatile recipe: you want almond-y buttercream? Use almond extract. Fruity buttercream? Try orange, strawberry, or pineapple extract. Why not chocolate extract or peppermint extract! Chocolate and vanilla extracts together taste great too. Frosts about 20-24 cupcakes or one 8" two-layer cake.