Rhubarb & custard blondies - Good Food Middle East

Ingredients

• 225g salted butter (or unsalted with a pinch of salt), plus extra for the tin
• 200g light brown soft sugar
• 100g caster sugar
• 150g plain flour
• 50g custard powder
• ½ tsp baking powder
• 3 medium eggs
• 250g white chocolate chips or white chocolate finely chopped
• 2 tsp vanilla extract
• 200g rhubarb (frozen, or canned and drained is fine)
• 75g caster sugar
• pink or red food colouring (optional)
• 4 tbsp ready-made custard (from a carton is fine, or made up from powder)