I want to serve this delicious cake to a group of twelve friends next week. What size baking dish (I'm thinking rectangular) would you use and h...

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I'm afraid I haven't made it in a size 1.5, but I am delighted you are keeping that cake going and growing! But let me see if I can help. A 9x2 inch round pan holds 8 cups, according to the fantastic Food Substitutions Bible. That means you need a pan holding about 12 cups to increase it by 50%. Choices handling that volume, according to the same book, are a 10x2.5 inch springform, 10x3.5 inch bundt (don't think this one is right for a bundt, however), or 13x9x2 inch rectangular pan. Bingo! Though it's not as elegant as a round, that sounds like the perfect choice. Or alternatively, the 10-inch springform should work out fine. My guess is that the rectangular cake will bake in about the same time at the same temp. For the 10-inch springform, since the batter will be deeper I would lower the temp by 25 degrees and give in an extra 15 min or so before you begin checking. Very well might take even longer. Happy baking!