Tuna and Potato Gratin (Gratin de Thon)
Why this recipe works
- Creamy, set layers: Parboiling the potatoes first helps them bake evenly, while the crème fraîche sauce settles between the slices rather than sitting on top.
- Simple savoury depth: Garlic, tuna and Gruyère bring enough flavour to make the gratin satisfying without needing a long-cooked sauce.
- Good for planning ahead: The gratin can be cooled, portioned and reheated, making it useful for lunches, batch cooking or a low-effort dinner later in the week.
Get the most out of this recipe
Timing notes
- Rest before slicing: Let the gratin stand briefly after baking so the sauce settles and the potato layers cut more neatly.
- Most of the time is hands-off: The active work is mainly slicing, parboiling and layering; the oven does the finishing.
Texture tips
- Drain the potatoes well: Steam-dry the parboiled slices before layering so excess water does not thin the sauce.
- Keep the sauce gentle: Warm the milk and crème fraîche over low heat and avoid boiling once the crème fraîche is added.
- Watch the cheese topping: Bake until the top is golden and the edges are bubbling; if it colours too fast, lower the oven to 190°C (375°F) for the final stretch.
Ingredient notes
- Choose a waxy, creamy potato: Yukon Gold-style potatoes hold their shape while still giving a tender, creamy bite.
- Use well-drained tuna: Flake the tuna into generous pieces rather than mashing it, so it stays distinct between the potato layers.
- Changing the dairy affects richness: Cream makes a fuller sauce than crème fraîche, while milder cheeses such as Emmental give a softer, less savoury finish.
Make-ahead tips
- Reheat gently: Warm leftovers in a 180°C (355°F) oven until piping hot, adding a small splash of milk if the gratin looks dry.
- Freeze in portions: Cool completely, wrap well and freeze individual portions; thaw overnight in the fridge before reheating.
Equipment you'll need
Ingredients
Instructions
- Heat the oven to 200°C (390°F). Peel the potatoes and slice them into thin rounds, about 3 mm thick. Bring a saucepan of water to the boil.
- Add the potatoes to the boiling water and parboil for 6 to 8 minutes until just starting to turn tender but still holding their shape. Drain well and leave to steam-dry for 2 minutes. Meanwhile, finely grate the garlic and grate the Gruyère.
- In the same saucepan over low heat, warm the milk with the garlic and black pepper until steaming but not boiling. Whisk in the crème fraiche until smooth, then take off the heat. Taste and adjust the pepper if you like.
- Flake the tuna into large pieces. In a baking dish, layer half the potatoes, then scatter over half the tuna. Spoon over about half the crème fraiche sauce, then repeat with the remaining potatoes, tuna and sauce.
- Top evenly with the Gruyère. Bake for 25 to 30 minutes until bubbling at the edges and golden on top. If it browns too quickly, reduce the oven to 190°C (375°F) for the final 10 minutes.
- Rest the gratin for 10 minutes before slicing and serving. This helps the layers set so it cuts neatly. Serve hot or warm.
Recipe notes
Tips
- Steam-drying the parboiled potatoes for a couple of minutes helps the sauce cling and keeps the gratin from turning watery.
- Keep the milk just below a simmer when you whisk in the crème fraiche so the sauce stays smooth and does not split.
- If serving to pregnant people, young children, older adults, or anyone immunocompromised, ensure the gratin is baked until piping hot throughout.
Substitutions
- Replace Gruyère cheese with Emmental cheese for a milder, nuttier topping.
- Replace Crème fraiche with cream for a richer sauce, keeping the heat low once added.
- Replace Yukon Gold potato with red potato for a slightly firmer slice.
Storage
- Refrigerate up to 3 days
- Cool completely, then cover and refrigerate. Reheat in a 180°C (355°F) oven for 15 to 20 minutes until piping hot; add a splash of whole milk if it looks dry. Freeze portions well wrapped for up to 2 months and thaw overnight in the fridge before reheating.
Ratings & reviews
Liked this recipe? Share your feedback to support our cooking community.
Tried this recipe?
Choose 1–5 stars. A comment is optional.
Stay inspired
Discover new recipes, seasonal favourites and cooking inspiration every day. Follow JustRecipes on Pinterest and Spillt.
Recipe overview
- Servings: 3 servings
- Total time: 1h 15min (25min active)
- Difficulty: Medium
- Cuisine: French
-
Allergens:
Fish Milk
Plan your meals and get a complete grocery list automatically.
Add to meal plannerEquipment you'll need
Got ingredients left?
Find recipes using ingredients from this recipe or what you already have at home.
Find recipes with these ingredients →
Cassoulet Toulousain (White Bean and Meat Casserole)
Slow-baked cassoulet with white beans, duck confit and sausages
Jansson’s Frestelse (Swedish Potato and Anchovy Casserole)
Swedish potato and anchovy casserole baked with double cream
Tepsi Baytinijan (Iraqi Aubergine and Minced Beef Bake)
Iraqi aubergine bake with minced beef and tomatoes
Enchiladas Verdes with Chicken and Crema
Baked chicken enchiladas with tomatillo sauce and crema
Gigantes Plaki (Greek Baked Giant Beans in Tomato Sauce)
Greek baked giant beans in tomato and olive oil sauce
Classic American Meatloaf with Brown Gravy
Baked beef meatloaf served with an easy brown gravy
Lentil Salad with Dijon Dressing (Salade de Lentilles)
Green lentil salad with Dijon dressing, shallots and parsley
Middle Eastern Salmon Bowl with Couscous and Tahini Dressing
Salmon bowl with couscous, salad and lemon tahini dressing
Arepas (Cornmeal Flatbreads)
Griddled cornmeal flatbreads with a crisp crust
Lobster Bisque
Smooth lobster bisque finished with brandy, tomato purée and cream
Latin Veggie Burrito Bowl
Veggie burrito bowl with black beans, peppers and avocado
Verdure in Pinzimonio with Bagna Cauda (Raw Vegetables and Warm Anchovy Dip)
Raw vegetables served with warm anchovy and garlic bagna cauda
Aligot de l’Aubrac (Stretchy Potato and Cheese Purée)
Stretchy potato purée beaten with Tomme cheese and crème fraîche
Gratin Dauphinois Traditionnel (Creamy Potato Gratin)
Creamy French potato gratin with garlic and nutmeg
Light Potato Gratin with Gruyère
Potato gratin with Gruyère, milk and garlic
Gratin de Légumes (French Potato and Leek Gratin)
Potato and leek gratin with cream, garlic and Gruyère
Brandade de Morue (Salt Cod and Potato Purée with Garlic)
Salt cod and potato purée with garlic, olive oil and cream
Flødekartofler (Danish Creamed Potatoes)
Danish creamed potatoes baked with garlic and nutmeg
You might also like
Rajma Chawal (Red Kidney Bean Curry with Rice)
Red kidney bean curry in spiced tomato gravy with basmati rice
Gammon Steak with Parsley Sauce and Mash
Pan-fried gammon with creamy mash and parsley white sauce
Ají de Gallina (Peruvian Creamy Chicken Stew)
Creamy Peruvian chicken stew with ají amarillo and walnuts
Vegetarian Nut Roast with Red Wine Gravy
Sliceable nut roast with mushrooms, carrots and red wine gravy
Steak au Poivre (Pan-Fried Steak with Peppercorn Sauce)
Peppercorn-crusted steak with creamy brandy sauce
Bamia (Slow-Cooked Lamb and Okra Stew)
Slow-cooked lamb and okra stew in tomato sauce
Make this recipe easier next time
AdvertisementThese tools help you get better results with less effort.
Misen 8-Inch Chef Knife
- AUS-10 steel
- Balanced design
- Less traditional feel
T-fal Specialty Nonstick Handy Pot with Glass Lid 3 Quart
- Easy food release
- Dishwasher safe
- Not induction compatible
WÜSTHOF Classic 8-Inch Chef's Knife
- Excellent build quality
- Reliable edge retention
- Expensive
WMF Mini Saucepan 16 cm with Lid
- High-quality stainless steel
- Even heat distribution
- Higher price point
Enjoy cooking with JustRecipes?
Add JustRecipes as one of your preferred Google sources to discover our recipes more easily across Google Search.
Add JustRecipes to GoogleEvery recipe on JustRecipes follows the same structured editorial process. Learn how recipes are created, validated, translated, illustrated, and continuously improved across the platform. How we create recipes.
