Help With Buttermilk Birthday Cake

Our answer

Normally to convert from a square cake pan to a round cake pan you would take the length of one side of the square pan and add 2.5cm (1 inch) to get the diameter of the round tin. However in this case the 23cm (9-inch) square tin is already quite large and a 25cm (10-inch) round pan is not particularly common, so we would suggest making one quantity of the cake mixture and baking it in a 23cm (9-inch) diameter round pan. Make sure the sides of the pan are at least 5cm (2 inches) deep. Fill the pan no more than 2/3rds full with batter (the leftover could be used to bake a couple of cupcakes).

Alternatively you could make up a double quantity of the mixture and bake it in a rectangular pan approximately 23 x 33 cm (9 x 13 inches). This would give you a good canvas from which to cut your cake.

The oven temperature is the same as for most cakes - 180c (350F, Gas Mk 4). The baking time for the 23cm round pan should be 30-35 minutes, but as ovens vary we suggest taking a peek at 25 minutes and testing the cake for doneness if the edges of the cake look like they are starting to shrink away from the sides of the pan. For a rectangular cake it should take 35-40 minutes but again it is worth quickly checking the cake after 30 minutes.