- To make the cake. Preheat the oven to 160ºC fan oven/180ºC/gas 5. Grease a 20cm cake tin.
- Beat together the butter and sugar. Add the egg and beat well. Add the single banana and beat well. Fold in the flour and zantham gum.
- Pour into the cake tin and bake in the oven for 30 minutes.Once cooked, remove from the tin, leave to cool and then break into chunks.
- Make the caramel sauce by gently melting all the ingredients in a small saucepan, stirring continually and simmering for 1 minute.
- Gently mix together the mascarpone and the cream.
- Layer all the cake, caramel sauce, cream, custard and bananas in sundae dishes. Sprinkle the nuts on top You may not need to use all the cake.