Transfer the leeks and sauce to a snug, ovenproof dish and use the back of the spoon to flatten the top. Sprinkle the breadcrumbs over the top and grate over a little more nutmeg. Slide the dish into the oven. Bake for 30-35 mins, till golden and bubbling. Let the dish sit for a few mins, then serve.

Preheat your oven to 200°C/Fan 180°C/Gas 6. Trim the roots and top 3cm off the leeks, then rinse the leeks under a cold tap to clean off any dirt and shake them dry. Slice into thin rounds. Peel the onion and finely chop it. Peel and thinly slice the garlic cloves. Pick the thyme leaves off their stalks and roughly chop.

Pour 1 tbsp olive oil into a medium pan and warm over a medium-low heat. Slide in the leeks, onion, garlic and thyme. Season with a good pinch of salt and pepper, and stir well. Pop the lid on the pan and cook gently for 10-15 mins, till very soft, stirring occasionally.

Stir 2 tbsp flour into the veg to coat them. Stir and fry for a further 1 min. Slowly trickle 400ml milk into the pan, stirring constantly as you add the milk, till the milk is fully combined with the flour into a thick sauce.

Bring to a bubble, then turn the heat down and simmer for 1-2 mins till slightly thickened. Take off the heat and stir in 1 tbsp wholegrain mustard. Grate in 1/4 of the nutmeg. Taste the leeks and add a little more nutmeg, salt or pepper if needed.