Cream butter and sugar and spread over the base of a deep cake tin. A loose bottomed tin can make it easier to remove the cake later - or you can line it with a piece of baking paper if you're nervous!
Arrange fruit on top. If you like you can put a glace cherry in the centre of each pineapple ring.
Make the sponge:
Cream butter and sugar.
Add beaten egg and vanilla.
Add sifted flour and baking powder alternately with milk (or use juice - not syrup - from the tin instead of milk).
Pour sponge mixture on top of fruit.
Bake at 180°C for 40 minutes, or until a skewer comes out clean.
Let stand for a few minutes before inverting onto a plate.