Heat oven to 180C/160C fan/gas 4. For the topping, beat the butter and sugar together until creamy.
Spread over the base and a quarter of the way up the sides of a 20-21cm round cake tin. Arrange pineapple rings on top but make sure you keep the syrup that the pineapple rings come in as you will need this later.
Cake
Place the cake ingredients in a bowl along with 2 tbsp of the pineapple syrup and, using an electric whisk, beat to a soft consistency.
Spoon into the tin on top of the pineapple and smooth it out so it’s level. Bake for 35 mins. Leave to stand for 5 mins, then turn out onto a plate. Serve warm with a scoop of ice cream.