HI guys,

I've been baking for a while now and always use two of the following recipes when baking a vanilla sponge for people.

http://www.bbcgoodfood.com/recipes/532634/grannys-victoria-sponge

http://www.bbcgoodfood.com/recipes/1997/classic-victoria-sandwich

However when using different sized tins i'm unsure as to whether I need to adjust the recipe or the heat of the oven. I kind of just wing it and double/ triple the mixture if the tins are larger

For example I've just used the Victoria sponge recipe in a 10x8 Rectangular tin (I didn't divide the mixture into two tins as it was just enough for the size of the tin)

I left the heat at 190/fan and baked for 30 minutes instead of 20 as the middle was still not cooked by that time (when i tested it with my metal skewer some mixture came off when i pulled it out). But what I ended up with was a light bouncy cake in the middle and lower & dry (almost crispy) edges !!!!!

Do I maybe need to turn the heat down to 180/fan or lower? Or is it because the mixture quantities need adjusting because i'm using a larger rectangle tin?

I generally use 8, 10 and 12 inch tins, I just want soft edges with a nice sponge

Any advice would be greatly appreciated as I will be tackling this size and shape cake again this morning! x

http://www.wilton.com/cakes/making-cakes/baking-serving-guide.cfm 

I stick more or less to this chart. If a recipe bakes one 8" 1.5-1.75" high layer, I double it for a 12" cake. The "problem" with bigger cakes is to get the middle to bake without burning the sides (like in your case). Many people use flat flower nails in the centre of big cakes as a heat core. Lowering the temperature towards the end and baking it slightly longer also helps. But every recipe is different and you have to experiment a little  to get it perfectly fine.