I make double quantities and use the same oven temperature and cooking times. My tins are the shallow ones, but are larger than those suggested in my recipe book. Double the quantity, for me, makes 3 sponges, which gives a lovely tall cake when sandwiched together. I recently made one with home-made
rhubarb and vanilla jam filling, chocolate coating on the top, and chocolate butter icing around the edge, covered in choccy sprinkles. Lovely.