French rhubarb tart

INGREDIENTS

• 700g thin forced rhubarb , ends trimmed
• 1 vanilla pod , seeds removed and reserved
• 50g caster sugar
• juice ½ lemon
• 225g plain flour , plus extra for rolling
• 25g ground almonds
• 2 tbsp icing sugar
• 140g cold butter , cubed
• 1 large egg yolk
• 250ml whole milk
• 4 large egg yolks
• 2 tbsp caster sugar
• 1 tbsp cornflour
• 1 tbsp plain flour
• 100ml double cream