You can use this as an accompaniment to your Sunday roast but we love it on its own, with plenty of pepper on top - and I can tell you something, it seems an odd combination, but its divine on top of a fluffy jacket potato!
Serves : 6 Prep/Cooking Time : 50 mins
Tip : Don't overcook the leeks as this will make them runny and watery and thin the sauce down when you put them into the oven.
In a large frying pan, heat up the oil gently, then add the onions. Cook for around 5 minutes on their own until they start to turn brown and caramelise.
Add the leeks and cook for a further 2 minutes, gently mixing the 2 vegetables together.
Place the mixture into a small ovenproof dish and set aside
Heat the oven to 220°C
In a small saucepan, add the milk, flour and butter and keep whisking quickly until the butter has melted and the flour has disappeared. Bring to the boil and you will see the sauce thicken up.
Keep whisking whilst the sauce bubbles and thickens right up then turn off the heat and stir in 3/4 of the cheese, then pour over the leeks
Using the remaining cheese, scatter over the leeks and then scatter over the breadcrumbs for a bit of extra crunch and texture
Finally, sprinkle the mustard powder evenly over the top, this adds a bit of bite to the flavour and place into the oven and bake for 20 minutes until bubbling.