Clean or peel the leek, celery, carrots, onions and mushrooms and cut into very fine strips. Mix the vegetables in a baking bowl and season well with salt and freshly ground pepper. Peel and press the garlic clove. Chop the basil. Stir in pressed garlic, basil and in about 1 tbsp of melted butter. Roll out the strudel dough, spread the vegetable mixture evenly on it and roll it up. Place the vegetable strudel on a baking tray lined with parchment paper and brush with egg yolk.
Bake in the oven at 200 °C (upper-lower heat) for about 25 minutes.
For the sauce, put the vegetable soup in a saucepan and boil a little, then add whipped cream and boil a little more.
Rinse the kitchen herbs, shake dry and chop finely. Blend the sauce with a hand blender, stir in the herbs and season to taste with salt and freshly ground pepper.
Cut the baked strudel into large pieces and serve with the sauce.
Our tip: As an alternative to fresh herbs, you can also use frozen ones – they also stand out for their fresh taste!