Classic Whoopie Pie vs Gypsy's Arm Cake Roll (Swiss Roll)

Both desserts lean on milk, butter, eggs and powdered sugar, but use them very differently. The whoopie pie creams butter into a cocoa batter leavened with baking soda, then sandwiches the baked cookies around a sweet, fluffy vanilla filling where powdered sugar, butter and shortening dominate. The Gypsy's arm whips eggs into a light sponge brightened with lemon zest, rolls it warm, and fills it with a cinnamon-scented pastry cream cooked from milk and finished with butter, or alternatively with jam. Powdered sugar here is simply a final dusting.