Taken from 'Baking and Desserts' cook book - Tasty Tip; To make homemade custard, pour 600 ml of milk with a few drops of vanilla essence into a saucepan and bring to the boil. Remove from the heat and allow to cool. Meanwhile, whisk 5 egg yolks and 3 tablespoons of caster sugar together in a mixing bowl until thick and pale in colour. Add the milk, stir and strain into a heavy-based saucepan. Cook the custard on a low heat, stirring constantly until the consistency of double cream. Pour over the rhubarb crumble and serve.