I have made 4 times the recipe in order to make a half sheet cake. Do I lower the degrees and bake time?
If you're making the same thickness of cake, and it's a relatively thin cake (suggested by the fact that you're using a sheet pan), you typically do not need to change the time and temperature. So if you've doubled the recipe and doubled the area of the pan, you don't need to make any changes.
A larger area cake will rise more as there won't be as much edge that will set before the rest has risen.
If it's a thicker cake (the batter is more than 1/2" / 1.25 cm deep before baking), you'll want to turn down the temperature and bake for a longer time. If the batter is an inch or more deep, you may want to consider cooling strips and/or a heating core.
Here's a highly rated recipe for a Red Velvet Cake in a sheet pan by Lee Drummond.
If you're in fact using a sheet pan, compare the quantities of your ingredients to hers. I wouldn't go any bigger in a sheet pan, or it will overflow. I know from experience, that makes a big mess.
- 2 1/2 cups cake flour
- 1teaspoon salt
- 1 cup buttermilk
- 1 teaspoon vanilla extract
- 1 teaspoon baking soda
- 2 whole eggs
- 1 1/2 teaspoons vinegar
- 1 1/2 teaspoons cocoa powder
- 1 1/2 fluid ounces red food coloring
- 1 cup shortening
- 1 3/4 cup granulated sugar
Make sure your ingredient quantites are in line with that.
She goes on to bake for 20 minutes at 350F (178C).