Rhubarb crumble recipe, with ginger, almonds, and cardamom custard

Ingredients

• 500 g rhubarb (500g (approx. 5 sticks))
• 100 g granulated sugar
• 2 tsp fresh ginger (grated)
• 1 tsp vanilla extract
• 1 tsp cinnamon
• 1 lemon
• A pinch salt
• 150 g flour
• 120 g unsalted butter (cut into dice (needs to be very cold))
• 50 g demerara sugar
• 50 g chopped almonds
• 50 g rolled oats
• 3 egg yolks
• 300 ml double cream
• 6 cardamom pods
• 1 ½ tbsp caster sugar
• 1 tsp cornflour