large sponge cake
If you have a recipe for a smaller tin then you just need to make more for
the larger tin. I went from a recipe for a 8 inch round to a 19x13 inch
tin. What I did was make the recipe for an 8 inch round. Pour the batter
in the tin and measure from the top of the batter to the top of the tin.
After I baked it and removed it from the tin I measure from the bottom of
the tin to the top of the tin. Measurement 2 minus measurement 1 gave me
how deep the batch should be before baking.
I did some rough math (16 * PI or 50 is the area of an 8 inch round; 19 *
13 or 247 is area of the new pan; 250 / 50 = 5; I need 5 times the
batter). Made more than enough batter (round down the results for the old
pan, round up the results for the new pan, round up the final results. If
the height of the batter was 1 inch in the old pan I poured enough in the
new pan so there was 1 inch depth.
If you are good with math you can actually calculate the exact difference
but I found that if the original recipe was not by weight, converting
things like 1/4 tsp or pinch was difficult. It was easier to multiply the
recipe by an even number and toss the extra (actually I experiment with
the extra batter in muffin tins).
I baked it at the same temperature or maybe a shade lower. I set the time
for the maximum the smaller cake usually took. I didn't even bother
checking it until the timer went off. Then I would check the cake with a
wooden toothpick every so often, right in the centre. I kept track of the
time and wrote it down. This way the next time I make the 19x13 cake I'll
know how long it takes. It actually took more than double the time.

Send email to: darrell dot grainger at utoronto dot ca
