To make Duchess Potatoes Casserole without a piping bag, use a zip top bag with a 1/2 inch hole cut in the corner for piping, or simply spread all of your prepared potatoes in the casserole dish and use the tines of a fork to create a grid pattern in the top of the potatoes (similar to the top of the mashed potatoes in our Creamy Fish Pie Recipe). Brush with butter, then bake.