Preheat the oven to 200°C fan.
Add the leeks and shallots to a large ovenproof frying pan with a little olive oil and a pinch of salt. Cook over a medium-low heat for 8–10 minutes, until really soft and sweet.
Add the garlic and cook for another minute, then stir through the flour. Cook for 30 seconds, then gradually pour in the milk, stirring as you go until smooth.
Crumble in the stock cube, add the Dijon mustard and plenty of black pepper. Simmer gently for 2–3 minutes, until the sauce has slightly thickened, turn off the heat, add ½ the cheese and mix to melt. Taste and season with salt.
Cook the tortelloni for around 2 minutes less than the packet instructions, then drain and stir through the creamy leek sauce.
If using an extra protein, stir through the shredded chicken or cooked salmon now. If using prawns, add them just before baking so they don’t overcook.
Mix together the breadcrumbs, the rest of the cheddar and Parmesan, salt, pepper then scatter over the top.
Bake for 10–15 minutes, until bubbling around the edges and golden on top.
Pop under the grill for a minute or two at the end if you want it extra crispy.
Serve with a big fresh side salad with plenty of lemon or a sharp vinaigrette to cut through the creamy sauce.
