Whenever I’m planning a dinner party menu, I’m always looking for a carb to round out the meal. Potatoes are always a safe bet, and this potato and leek gratin is a recipe I often gravitate towards because it goes with just about anything.
If you’re familiar with gratin dauphinoise, you’ll feel right at home with this recipe. Like the classic French dish, thinly sliced potatoes are baked in cream until tender and golden. The addition of leeks gives the gratin a gentle sweetness, while the garlic and thyme-infused cream balances the dish with a subtle savoury depth. This gratin pairs just as well with roast chicken as it does with pork, lamb or slow-cooked beef. It’s also relatively inexpensive to make and can be prepared well in advance, which takes a lot of the stress out of hosting.
In this Post
- What is a gratin?
- Ingredients
- How to make Potato & Leek Gratin
- Variations & Substitutes
- Storing & Reheating Leftovers
- Frequently Asked Questions
- The Recipe
What is a Gratin?
A gratin is a dish that is baked until a golden crust forms on top and can be made from potatoes and other vegetables, as well as pasta and seafood. One of the most well-known gratins is gratin dauphinoise, a classic French gratin of potatoes cooked in cream. While some gratins rely on cream alone, others are baked with cheese, like my baked cauliflower cheese recipe.
Ingredients
Potatoes: Floury potatoes work best for this gratin as they absorb the cream and become beautifully tender during baking. I used Agria potatoes, which are widely available in New Zealand and have enough starch to help thicken the cream while still holding their shape. Other varieties commonly found elsewhere are Maris Piper or Russet potatoes.
Leeks: You’ll need two large leeks for this recipe. The exact size isn’t critical, but aim for enough to be noticeable throughout the gratin without overwhelming the potatoes. Once cooked, the leeks soften into the cream and add a gentle sweetness to the finished dish.
Cream and milk: Using a combination of cream and milk keeps the gratin rich without becoming too heavy. As the potatoes cook, they release starch into the dairy, creating a silky sauce that coats each layer.
Garlic: Rather than chopping or crushing the garlic into the gratin itself, the cloves are first rubbed over the baking dish before being gently infused into the cream. It’s a subtle technique, but one that adds a delicate garlic flavour throughout the dish without becoming overpowering.
Thyme: Fresh thyme is infused into the cream alongside the garlic before being removed. The flavour isn’t immediately obvious, but it adds a subtle savoury depth that balances the sweetness of the leeks and richness of the cream.
How to make Potato & Leek Gratin
ONE: Cook the leeks in butter over medium heat until soft but not coloured, around 5-8 minutes.
TWO: Combine the cooked leeks with the raw sliced potatoes in a large bowl and season with salt.
THREE: Rub the cut garlic cloves over the baking dish, then grease with butter. Transfer the potatoes and leeks to the dish and spread into an even layer.
FOUR: Heat the cream and milk with the garlic cloves and thyme until just below a simmer.
FIVE: Strain the cream and milk mixture and pour over the potatoes.
SIX: Cover with baking paper and foil and bake at 180°C (160°C fan) for 1 hour 30 minutes. Remove the foil and baking paper and continue baking for 20–30 minutes, or until a knife slides easily through the potatoes and the top is golden brown. Rest for 10-15 minutes before serving.
Variations & Substitutions
Swap the Leeks
Leeks bring a gentle sweetness to this gratin, but onions or shallots can be used instead. Onions will give the dish a much stronger flavour and can even be caramelised before adding them to the potatoes if you’d like a little extra sweetness. Shallots are a more delicate option, adding a subtle onion flavour that won’t dominate the dish.
Change the Herbs
I like using thyme in this gratin because its flavour is subtle and works with just about anything. That said, you can easily swap it for other herbs to bring the flavours of your meal together. If you’re cooking lamb with rosemary or chicken with sage, try infusing the cream with those herbs instead.
Add Cheese
If you’d like to add cheese, sprinkle grated Gruyère, Parmesan or another melting cheese over the top of the gratin during the final 20-30 minutes of baking.
Storing & Reheating Leftovers
Storing & Reheating Leftovers
The good news is that this gratin keeps exceptionally well. In fact, I found the texture was even better the next day once the potatoes had absorbed more of the cream. The entire dish can be prepared a day in advance and reheated before serving, and it’s also much easier to cut into neat portions while cold.
Store any leftovers covered in the refrigerator for up to 3 days.
To reheat, bake at 180°C for 20-30 minutes, or until heated through. Individual portions can also be reheated in the microwave.
Frequently Asked Questions
Yes. The gratin can be assembled several hours in advance and kept in the refrigerator before baking. Just be aware that the potatoes may discolour slightly if left overnight before cooking.
Not necessarily, but it makes it much easier to get even, very thin slices of potato. If using a knife, make sure it is sharp, and take your time to slice the potatoes evenly.
Yes. Allow the gratin to cool completely, then wrap well and freeze for up to 3 months. Thaw overnight in the refrigerator before reheating in the oven until hot throughout.
The Recipe
I’d love to hear how you get on with making this recipe if you try it and how much you enjoyed eating it! Leave a review below for me to read, or tag me on Instagram if you share a photo.
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Potato & Leek Gratin
A rich and comforting gratin made with layers of potatoes, leeks and cream, baked until tender and golden.
- Total Time: 2 hours 40 minutes
- Yield: 8–10 servings 1x
Ingredients
- 20 grams butter, plus extra for greasing the baking dish
- 2 large leeks, trimmed, washed and thinly sliced
- 1.2 kilograms Agria potatoes, peeled and thinly sliced with a mandolin
- 16 grams fine sea salt
- 2 garlic cloves, halved
- 600 millilitres cream
- 200 millilitres whole milk
- 4 sprigs fresh thyme
Instructions
- Preheat the oven to 180°C (160°C fan bake).
- Melt the butter in a saucepan over medium heat. Add the leeks, cover with a lid and cook for 5-8 minutes, stirring occasionally, until softened but not coloured.
- Place the sliced potatoes and cooked leeks in a large bowl. Add the salt and toss well to combine.
- Cut the garlic cloves in half and rub them all over the inside of a baking dish approximately 30cm x 20cm. Butter the dish, then transfer the potato and leek mixture to it, spreading it into an even layer.
- Add the garlic cloves, cream, milk and thyme to a saucepan and gently heat over medium heat until just below a simmer. Strain the cream mixture over the potatoes and gently press them down so they are mostly submerged.
- Cover the surface of the gratin with baking paper, followed by a layer of foil. This traps moisture and prevents the top from browning before the potatoes have had time to become tender. Bake for 1 hour 30 minutes. Remove the foil and baking paper and continue baking for 20-30 minutes, or until a knife slides easily through the potatoes and the top is golden brown. Rest for 10-15 minutes before serving.
Notes
- The 16 grams of salt used in this recipe is approximately 1% of the combined weight of the potatoes and leeks. If you’re unsure of the total weight, it’s better to season a little more conservatively and add extra salt to taste after cooking.
- Cooking times can vary depending on the thickness of your potato slices and the depth of your baking dish. The gratin is ready when a knife slides easily through the centre with very little resistance.
- A mandolin isn’t essential, but it does make it easier to achieve evenly sliced potatoes, which helps the gratin cook more evenly.
- Prep Time: 25 minutes
- Resting Time: 15 minutes
- Cook Time: 2 hours
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