These gorgeous cheesy creamed leeks are the perfect side dish for a roast dinner or special occasion like Christmas or Thanksgiving. The sliced leeks are sauteed until buttery soft in butter, a little oil, and thyme, and then topped with a thick and cheesy roux seasoned with lots of black pepper and a smidgen of Dijon mustard. The whole thing is then baked until the top is golden and bubbly, and simply irresistible.

I've made this recipe multiple times now, and every time it blows my mind how such a simple dish can be so mouth-wateringly moreish! You could also add some roasted cauliflower before baking for an amazing side dish.

Serve these cheesy creamed leeks with roast potatoes, cauliflower cheese, stuffing balls, and your main of choice! You could also level up this dish with my potato and leek gratin.

Ingredient Notes

The exact quantities are listed in the recipe card below, but here are some notes on the key ingredients and possible substitutions:

• Leeks: Make sure to wash these thoroughly - leeks are notorious for trapping dirt between their layers. If you can't find leeks, green onions, or shallots could work as a substitute, though the flavor won't be quite the same. If you can't get leeks, try my cauliflower cheese as a side dish instead.
  
• Butter: Adds richness to the dish and helps soften the leeks. Use unsalted butter so you can control the salt level.
  
• Milk: We use milk for the roux - you could use half milk and half heavy cream to make this a really indulgent and creamy dish.
  
• Plain flour: A few tablespoons of plain flour, cooked off in the butter, are needed to help the sauce get really thick and creamy.
  
• Cheese: Extra-mature cheddar brings sharpness and depth to the dish while also giving the cheesy leeks that perfect golden bubbly topping.
  
• Herbs & Seasonings: Thyme adds lovely earthy undertones to the leeks, but feel free to use fresh herbs if you have them on hand. A teaspoon of Dijon mustard is also a great addition.

Variations & Substitutions

• Add Other Vegetables: Bulk up this side dish by adding some roasted cauliflower to the sauteed leeks before pouring over the cheese sauce, or level it up by making this potato and leek gratin instead.
  
• Instead of making a roux, you could just combine heavy cream with the Dijon mustard and cheese before pouring it over the sauteed leeks and then baking. The sauce would be thinner, but still pretty delicious and an easy way of achieving a similar result.

How To Make These Cheesy Creamed Leeks

Here's a short overview to making your cheesy creamed leeks - scroll down to the recipe card at the bottom of the page for the full overview and ingredient quantities needed.

1. Prep the Leeks

It's always a good idea for wash your leeks thoroughly, as it's easy for dirt to be embedded in all the layers of the vegetable. To do this, cut your leeks in half lengthways and wash under cool running water. Then, cut the tops and ends off your leeks and slice them thinly.

2. Cook the Leeks

In your skillet, melt the butter in the olive oil and sauté the leeks for 6-8 minutes until softened and fragrant, stirring often. Add the minced garlic and thyme, cooking for another minute or two. Then, set the sauteed leeks aside.

If you don't have a skillet, transfer the leeks to an oven-safe dish now.

3. Make the Cheesy Sauce

Melt the remaining butter in a saucepan, then add the flour. Cook off the flour in the butter for a couple of minutes (it will form a doughy consistency), then slowly whisk in the milk until you have a smooth sauce with no lumps.

Remove the pan from the heat and then slowly add two-thirds of the grated cheese a handful at a time and whisk it into the sauce. Doing it this way prevents the cheese from splitting and curdling in the roux sauce.

4. Assemble and Bake

Pour the cheese sauce over the sauteed leeks and stir together to ensure the leeks are fully coated. Then, top with the remaining cheese, and bake for 25 minutes at 200°C (390°F). Grill for the last 5 minutes to achieve a crispy, golden cheese topping.

Top Tips / Chef's Notes

• Don't rush the leeks: Cooking them slowly helps bring out their natural sweetness.
• Taste as you go: The cream and cheese add saltiness, so season gradually to avoid over-salting.
• Go fresh if you can: Fresh thyme and rosemary elevate the dish, but dried herbs work just as well in a pinch.
• Cheese consistency: Grate the cheese yourself for better melting; pre-shredded cheese often contains anti-caking agents that can affect the texture.

Storage

• Fridge: Store leftovers in an airtight container for up to 3 days. Reheat in the oven or microwave until warmed through.
• Freezer: Cream-based dishes don't freeze well, as the sauce may separate when reheated.

FAQs

Can I make this ahead of time?
Yes! You can prepare the creamed leeks up to the point of baking, store them in the fridge, and bake them when you're ready to serve.

Can I use other vegetables?
Absolutely. Try adding roasted cauliflower, mushrooms, spinach, or even some sautéed asparagus to the mix.

What's the best cheese for this recipe?
Extra mature cheddar is a classic choice, but Gruyère, Parmesan, or even a mix of cheeses work beautifully.