Mix all the ingredients in a bowl.
To shape & bake the strudel
Remove the pastry from the fridge shortly before use, carefully separate the pastry sheets and place on a damp tea towel. Brush each one with a little butter and stack the sheets on top of each other. Spread the filling on top, leaving approx. 2 cm free around the edges. Roll up the strudel, place it seam-side down on a baking tray lined with baking paper, brush with butter.
Bake for approx. 45 mins. in the centre of an oven preheated to 200°C, brushing several times with the remainder of the butter. Serve cool.
Using a whisk, combine the milk and remaining ingredients and bring to the boil over a medium heat, stirring constantly. As soon as the mixture thickens, remove the pan from the heat and stir for a further 2 mins. Pour the custard through a sieve into a sauce boat and serve warm with the strudel.