Transfer the batter to the prepared pan(s). Bake the sheet pan cake for 18-22 minutes OR until a toothpick inserted in the center comes out clean or the temperature in the center of the cake is 200-205˚F (93-96˚C). The round cakes will take 25-35 minutes. Use the same testing to determine doneness.
Add the remaining 1½ cups powdered sugar and whisk until smooth. You want a nice spreadable consistency. If the icing seems too thin, add a bit more powdered sugar, if too thick, add more half and half, one teaspoon at a time.
See Café Tips above in the post for further instructions and more detailed tips to ensure success.
Half and half is an American convenience product often used in coffee. It's a mixture of half milk and half cream. You can substitute half milk and half cream or just use one or the other.
Recipe adapted from Food 52.