Preheat the oven to 180C. Cut the rhubarb into roughly 4cm pieces
Place into a large pan in one layer and sprinkle over ¼ of the sugar.
Pour over your water, bring to a simmer and cook for about 5 or 6 mins, then turn off the heat and leave to cool slightly.
Meanwhile, in a food processor combine the flour and remaining sugar. Cube up the butter, add and pulse until the mixture resembles breadcrumbs.
Remove the rhubarb from the pan using a slotted spoon and transfer it to a baking dish. Pour the crumble mixture on top, then sprinkle over the oats.
Bake in the oven for about 25 to 30 mins until golden brown. Leave to rest for 5 mins before serving.
Whilst the crumble bakes, make the custard. Add the milk, sugar, ginger and vanilla extract to a saucepan and bring up to a gentle simmer, stirring to dissolve the sugar, then turn the heat to minimum.
While the milk is warming, whisk the egg yolks in a bowl. Now add the egg yolks bit by bit to the milk, whisking each time, until they’re all added.
Keep warming gently and stirring until the custard is glossy and coats the back of a spoon.
Serve up a big spoon of the crumble and drizzle over the custard.
