I recently tried baking a separated egg sponge cake in a 13x9 pan. The recipe called for 5 large eggs separated, 1 cup flour, 1 cup sugar, 1/3 cup milk and 11/4 tsp baking powder. The batter rose well in my 350 oven and was done in 25 minutes, way before the expected 35-45 minutes baking time. Halfway throughout the baking time, I had lowered the temperature to 325, to prevent browning of the top.
However, in parts, the cake sank around the middle and at one place near the edge. I am looking for an explanation for this so that I can take care of the problem next time.
1)was it because I lowered the temperature halfway in the process- should i have kept it at 350 all along and covered with foil? Does a foam cake like this need higher or lower temperature to set?
2) should I have used a lowered temperature of 325 like biscuit de savoie throughout for slow and even baking?
3) that I need to use less baking powder or none at all - recipe requires it.
4) that the cake was baked in a 13x9 flat pan which affects structure - again that was a part of the recipe.
5) one more thing that keeps on bugging me,could it also be that the egg white did not completely and perfectly fold in the egg yolk mixture causing the cake to deflate where there was extra egg white?
Please help.I was thinking of baking it at 350 next time with less baking powder and not change temperature at all. This cake needs to be baked in a sheet pan so I cannot change that parameter.
Please help me so I can figure out which parameter to change