This creamy leek and mustard gratin is a proper comfort food side dish that brings a warm, rustic elegance to the table. I’ve been making versions of it for years, and it never fails to impress guests at a Sunday roast or alongside smoky barbecue meats. The sweetness of the softened leeks pairs perfectly with the tang of wholegrain mustard and the richness of cream and cheese. It’s a dish that feels indulgent yet still light enough not to overwhelm a plate piled high with beef, chicken, or pork.
What I love most about this gratin is how versatile it is. It slots in beautifully next to something hearty like beef short ribs with ale and treacle glaze or a simple roasted chicken. I’ve even served it at barbecues where it’s held its own next to sticky honey mustard BBQ pork skewers.
Preparing the leeks for a silky base
Leeks are one of those ingredients that can transform a dish when cooked with care. I always start by slicing them into rounds, then washing thoroughly to remove any grit hiding between the layers. Cooking them gently in butter until they’re soft but not coloured gives the gratin its sweet, mellow base.
This technique is key. If you rush the leeks, they won’t develop that lovely buttery softness. I’ve found they need around 8–10 minutes on a medium-low heat, and I always add a splash of water to create a little steam, which speeds things along without burning the edges.
Building flavour with the mustard and cream
Once the leeks are tender, I stir in wholegrain mustard and a little English mustard powder for extra depth. The combination adds warmth without overpowering the delicate leeks. Pouring over double cream and letting it simmer for a minute or two creates a luscious sauce that’s ready for the oven.
For a richer layer of flavour, I sometimes add a hint of nutmeg or swap part of the cream for crème fraîche. It’s these little touches that make the gratin sing alongside bold main dishes like beef skirt steak with horseradish and chive butter.
Topping the gratin for golden perfection
The topping is where this dish becomes irresistible. A mix of fresh breadcrumbs, grated mature Cheddar, and Parmesan gives you a crust that’s crisp on top but still allows the creamy filling to bubble underneath. For extra crunch, I sometimes scatter over a few crushed hazelnuts or almonds.
Once baked, the gratin comes out of the oven with a golden, cheesy crust that contrasts beautifully with the soft leeks beneath. Pair it with BBQ chicken thighs with sticky apricot glaze for a meal that feels balanced and satisfying.
My Wine and beer recommendations
When I serve this gratin, I often pour a glass of Chardonnay. Its creamy texture and subtle vanilla notes complement the richness of the leeks and cheese without clashing with the mustard’s slight tang. If you prefer beer, a Belgian Leffe blonde ale works wonders. It’s delicious, slightly fruity, and refreshes the palate between bites.
If you’re planning a barbecue spread, this gratin also holds up alongside robust reds like a soft Pinot Noir, especially if the main is something like grilled bavette steak with garlic chilli butter.
This gratin deserves a spot on your table
This creamy leek and mustard gratin works equally well as part of a Sunday roast, a festive dinner, or a relaxed summer BBQ. It’s one of those sides that bridges the gap between winter comfort and lighter seasonal fare. The buttery leeks, rich cream, and punchy mustard make it an excellent match for smoky dishes like BBQ roasted sage, garlic and Parmesan cheese potatoes or even vegetarian favourites from our halloumi skewer roundup.
I’ve also taken it to potlucks and family gatherings where it’s always one of the first dishes to disappear. It’s simple to prepare yet feels special enough to earn a place at any feast.
Creamy Leek and Mustard Gratin
Ingredients
- 4 Leeks large, sliced into 1cm rounds
- 50 g Butter unsalted
- 1 tbsp Wholegrain Mustard
- ½ tsp English mustard powder
- 300 ml Double cream
- 100 g Cheddar mature, grated
- 50 g Parmesan Cheese finely grated
- 50 g Fresh breadcrumbs
- Sea Salt to taste
Instructions
- Melt the butter in a large frying pan over medium-low heat. Add the sliced leeks with a pinch of salt and cook gently for 8–10 minutes, stirring occasionally, until soft but not coloured. Add a splash of water if the pan starts to look dry.
- Stir in the wholegrain mustard and mustard powder, then pour over the double cream. Season with a little pepper and nutmeg if using. Simmer for 2 minutes to thicken slightly. Taste and adjust the seasoning as needed.
- Preheat the oven to 190°C (170°C fan). Transfer the creamy leeks to a buttered ovenproof dish. Mix the Cheddar, Parmesan, and breadcrumbs in a bowl, then scatter evenly over the leeks.
- Bake in the oven for 25–30 minutes until the top is golden brown and crisp. Serve straight from the oven as a side dish.