Hi, Astrid! If you look in your RHC, I’d scope that wedding cake. My guess is it has a 10” tier and will give you the exact everything to use.
Meanwhile, if you decide to just go from the ‘regular’ recipe, you can double it. The volume of a 9x2” pan is 63—2x63 = 126. The volume of a 10x2” pan is 78, and the volume of an 8x2” pan is 50. 78 + 50 = 128. Put about 40% of the batter in the 8” pan and 60% of the batter in the 10” pan.
This is something I learned recently: 1 tier = two layers of the same size. So, if you’re making a two-tiered cake, with one tier being 10” and another being 8”, that would be 4 layers. In that case, you’d use 4x recipe. If you’re making to layers, you’d use 2x recipe.
If you go with the ‘regular’ recipe, you might want to decrease the baking powder by 1/8”—again, it’s experimental—but it might help keep a dip from forming. The decrease might give you a small dome on the 8” layer, but you can trim a dome. (Maybe you can put it upside down in a dip—ha ha.) If you bake the pans one at a time, bake the 8” first—this will let the 10” expel some leavening and gain strength.
Good luck—let us know how it happens!!! The best advice, though, is to scope that wedding cake. It’s the tropical wedding cake or something—banana is not in the title—but there’s sure to be accurate measurements there for a larger size pan.