Leche flan is usually baked in a llanera but for leche flan cake, you’ll want to use a deep pan to show off the cake’s layers.  I like — and recommend — using 2 6x3 inch round pans. You can also use 2 8x2 inch round pans but note that the layers will be thinner. I’ve never used a 9x13 inch rectangular pan because I think the layers will be too thin, but mostly because we don’t own a cake platter big enough to invert the cake onto.