My AGA is a regular range, not a cooker, but I have read a bit on the cookers. It seems that suggestions about how to bake cakes depend on how many ovens your AGA has. It also matters what kind and size your cake is. A common suggestion is to put the cake on the oven floor or bottom runner and to put the cold shelf above the cake to deflect heat from the top. A cold roasting pan can substitute for the shelf. That should help with the overbrowning. Others suggestion changing to one of the cooler ovens after some initial baking time. If you google "AGA cake baking," you'll probably find a number of other suggestions more specific to your model. Hopefully someone with actual experience will chime in.