Leek and Potato Gratin with Tarragon

Leek and Potato Gratin with Tarragon

This leek and potato gratin is a vegetable-forward side dish with tender potato layers, plenty of soft leeks, and the gentle anise note of tarragon. Greek yogurt and semi-skimmed milk replace the usual heavy-cream base, while a modest amount of Gruyère creates the golden top that makes a gratin feel special.

It is designed as a side rather than a stand-alone main, making it a natural partner for roast chicken, fish, or a simple lentil dish. The tarragon and leeks give this page a clearer flavour focus than a classic dauphinoise-style potato gratin.

Flavor Profile

Leeks become mellow and slightly sweet as they cook, which works especially well with the savoury depth of Gruyère. Tarragon brings a fresh, faintly liquorice-like note that stops the potato layers from feeling too rich. A small amount of nutmeg supports the creamy sauce without becoming the dominant flavour.

How It Comes Together

Start by washing the sliced leeks well. Grit often sits between the layers, so swish them in cold water and lift them out rather than pouring the water away over them. Soften them gently with garlic and tarragon while the oven heats.

Whisk Greek yogurt with milk before assembling; bringing the yogurt toward room temperature first helps the mixture stay smooth. Alternate potatoes, leeks, and sauce in the dish, cover for the first part of baking, then uncover to brown the cheese. The covered stage cooks the potatoes through, while the final uncovered stage gives the top its gratin crust.

Chef's Tips

Choose a waxy potato such as Charlotte, Anya, or another salad-style potato. It holds its shape better than a floury baking potato and gives neat, tender layers. Use a mandoline carefully if you have one, or take time to cut the potatoes to an even thickness with a sharp knife.

Do not rush the resting time. Ten minutes lets the sauce settle around the potatoes, making the gratin much easier to portion. If the top browns before the potatoes are tender, loosely cover the dish again and continue baking until a knife slides through the centre without resistance.

Ingredient Highlights

The high proportion of leeks means each portion contains around 150 g of vegetables, not just potatoes and dairy. Greek yogurt adds protein and creaminess with substantially less saturated fat than double cream. Gruyère is used as a finishing ingredient rather than throughout every layer, so its nutty flavour still comes through without overwhelming the tarragon.

Low-Cholesterol Notes

Replacing double cream and butter with Greek yogurt, semi-skimmed milk, and a small amount of olive oil keeps this gratin comparatively light for its style. Cheese still contributes saturated fat, so treat the listed portion as a side dish and pair it with a lean protein and additional green vegetables.

Easy Swaps

Mature cheddar, Comté, or a reduced-fat hard cheese can replace Gruyère. Use thyme or chives if tarragon is unavailable; both are good with leeks, though the result will have a different character. For extra vegetables, layer in thinly sliced courgette or mushrooms with the leeks, reducing the potato slightly so the dish is not overcrowded.

Make-Ahead & Meal Prep

Assemble the gratin a day ahead, cover tightly, and refrigerate. Bake it just before serving for the best top. Leftovers keep for up to 3 days and reheat well in a 180°C / 160°C fan oven, covered, until hot through; uncover for the final few minutes to re-crisp the cheese.

Serving & Goal Fit

One serving is about 340 g of leek and potato gratin. It works best alongside grilled chicken breast, fish, tofu, tempeh, or lentils to make a balanced meal. On a training day, keep the portion as written or add 50 g cooked rice if you need more carbohydrate. On a rest day, use a slightly smaller potato portion and add broccoli, green beans, spinach, peas, mushrooms, onions, courgette, or tenderstem broccoli alongside.