Humming bird cake

Hi, I am hoping to make a humming bird cake as the bottom tia of a wedding cake. the recipe i have is to be made in a 20cm square tin but i would like to make it in a 25cm round tin and double the recipe. my question is how long would i cook it. for the time for the 20cm tin is 1hr at a 180 c

Your double mixture will give you a cake that is 1.6 times as deep as the original cake so it's probably going to be pretty deep. I wouldn't cook a deep cake at 180 because the outside is going to cook before the inside. I'd turn the oven well down down -maybe as low as 160. It would probably take round 1 hour and 20 before testing It's well worth doing a practice run with a wedding cake, particularly when you're adjusting temperatures. Also for a big cake, bake even strips are excellent for spreading heat and giving you nice flat cake that doesn't need much trimming. Have you thought about making the cake in two layers with filling between them?

I was going to make it also for daughter's wedding but my cake decorating tutor talked me out of it saying it will be too moist for the sugarpaste icing- it might be ok with butter icing though.