Welcome to the Cake Decorators Q&A

I’m currently baking a 15” square vanilla sponge cake, I used the answer to a previously asked question on here to assist me but just wondering how long you would advise baking this for?

I used the calculator in the resources section to up scale my recipe which is the classic vanilla recipe of 500g SR Flour, butter and caster sugar with 8 eggs, 6tbspns milk and a tspn of vanilla. The calculator suggested I needed to multiply all ingredients by 3 to bake a 15” square.

I’ve baked it for 3hrs at 140 degrees and am just taking it out of the oven now. Would you agree or suggest a different temp or time?

Hi Cheryle Beattie

I usually bake very large cakes at 130c fan for a little longer than the recommended time. However, every oven is different, and the given time or temperature can vary from oven to oven.

If it’s a first time baking an unusually large cake, keeping an eye and nose on its progress is the best way to determine the best timing and temperature for your own oven.

I find baking layers using 1.5” deep sheet cakes less time consuming, and less stressful than baking one deep cake. It also does away with the need to evenly cut layers for stacking.

I hope your deep 15” cake has turned out good. 🙂

Thank you. It is baked around most of the cake but the centre is underbaked. Not a massive issue for the cake I’m making, it’s a castle with a wall around the perimeter of the cake board so I will use this for the wall and bake more for the building part. My problem is I use a stainless steel cake tester, I’ve also used a bamboo skewer in the past and when you take it out clean the cake is supposed to be baked but mine comes out clean even if it’s underbaked which is so frustrating cos I just can never tell. It’s that really close texture that looks damp inside 😩

I tend to press the top , middle of the cake to check for doneness. It should feel firm but spring back immediately.

Square cakes, especially if extra large and deep, do take a lot longer. The corners have to protected by double lining the cake pan to prevent burning. It does help to reduce the temperature and bake on for a little longer.

I love the philosophical way you’ve dealt with the finished bake. Hope all goes well with the remaining bake and the decorating. 🙂

Ps. I think 3 hours 45mins at 130c fan or 150c non fan would be adequate. However, as stated earlier, keep your eyes and nose on it.