Having run the cake table at my daughter's school last year, I can say that there are two types of optimum bake sale fare: small, individual pieces that look cute and fetch high unit-prices and sheet cakes that can be made without effort or dexterity and sliced up easily. This recipe fits the latter category and has the added virtue of appealing to parents and grandparents who feel that something from the sale should be gratifyingly old-fashioned. The fresh ginger is a modern touch, admittedly, but I always keep some in the fridge and wanted to try it in a less contemporary, pan-Asian way one day (it worked.) The lemon icing may not be conventional either, but there is another starkly practical reason for it: brown things — if they're not gooily chocolate — don't sell so well; and the lemon spruceness of the topping is perfect with the musky sweetness beneath it.