Preheat the oven to 180C/350F/Gas 4.
For the crumble topping, place the flour and butter into a food processor and pulse until the mixture resembles breadcrumbs, then stir in the sugar and ground ginger.
For the filling, melt the butter in a saucepan, add the rhubarb, sugar and ginger and simmer over a low heat for 6-8 minutes, or until the rhubarb has softened.
Spoon the filling into a gratin dish, sprinkle the crumble topping over the rhubarb and bake in the oven for 10-15 minutes, or until the topping is golden-brown and crisp.
For the crème anglaise, heat the milk, cream and vanilla pod together in a saucepan, but do not allow to come to the boil.
In a separate bowl, whisk together the egg yolks and sugar, then pour the hot milk over the eggs and whisk until well combined. Pour the mixture back into a clean pan and heat, stirring frequently until the mix has thickened enough to coat the back of a wooden spoon.
Serve the crumble with a generous drizzling of the crème anglaise.
