Rhubarb & custard crumble cake - Good Food Middle East

Ingredients

• 125g butter , softened, plus extra for the tin
• 400g rhubarb , chopped into 1cm chunks
• 200g golden caster sugar
• 150g self-raising flour
• 50g quick-cook polenta
• 3 tbsp custard powder
• ½ tsp baking powder
• 2 eggs
• 1 tsp vanilla extract
• 125ml soured cream
• icing sugar , for dusting
• double cream , to serve (optional)
• 100g golden caster sugar
• 60g plain flour
• 2 tbsp custard powder
• 1 tbsp quick-cook polenta
• 50g butter , cubed