I'm making a recipe from GBBO Season 2. It's the "berry crumble traybake," and it calls for a 26cm x 20 cm (10 1/2in x 8 inch) pan. Never heard of that size pan. Per Joy of Baking, 10x10x2 (which I don't have) is 12 cups and 11x7 (which I do have) is 6 cups. I would love to double the recipe, but I can't go larger than my roughly 13x9 springform lasagna pan (14 cups). Thoughts? Thanks!