Rhubarb and strawberry crumble with Horlicks custard

Ingredients

• 400g rhubarb, cut into 3cm batons
• 400g strawberries, halved or quartered
• 40g demerara sugar
• 125g plain flour
• 60g Horlicks Original
• 35g ground almonds
• 30g rolled oats
• 170g chilled unsalted butter, grated or diced
• 75g demerara sugar
• ¼ tsp salt
• 290ml whole milk
• 3 egg yolks
• 1 vanilla pod, split in half and seeds scraped out
• 2 tbsp caster sugar
• 30g Horlicks Original
• 1 tsp cornflour