The truffle is not a garnish here. It is the bechamel. All 95 grams of Bordier's Perigord black truffle butter go into this sandwich: 65 grams cooked into the roux, the rest melted and brushed over the toast. What comes out is a croque-monsieur where the truffle is carried by the sauce through every layer rather than shaved on at the end and lost under the grill. Thirty minutes of preparation and five minutes in a hot oven.
At a glance
- Difficulty: Medium
- Serves: 4
- Active time: 30 minutes
- Cook: 5 minutes at 200°C / about 390°F
- Key ingredient: Perigord Black Truffle Bordier Butter
Why this works
Bordier introduced the Perigord black truffle butter in 2024, at 3.4% Tuber melanosporum. That percentage matters. Truffle aroma is volatile and fat-soluble, which is the reason truffle is almost always served with butter, cream or egg rather than on its own. Suspending it in hand-churned Breton butter is about the most efficient carrier there is, and it means the aroma survives being cooked, which shaved fresh truffle does not.
Putting that butter into a bechamel is the smart move. A roux holds the butter in place: the flour binds it, the milk dilutes it evenly, and the finished sauce spreads truffle through every square inch of the sandwich instead of concentrating it in one bite. The second use, brushing melted truffle butter onto the outer faces of the toast, is what browns the outside. Everything else in the build is chosen not to fight it. Country bread cut thick has enough structure to carry a wet sauce, and Salers or Laguiole, both firm AOP cows' milk cheeses from the Massif Central, bring depth without the sharpness that would crowd out the truffle. Five minutes at 200°C is only long enough to melt the cheese, because the bread is already toasted.
Ingredients
The truffle butter is used twice, so weigh out the 65 g for the bechamel before you start and keep the remainder aside for the toast.
| Ingredient | Metric | US |
|---|---|---|
| Bordier butter with black Perigord truffles | 95 g | 3.4 oz |
| Thick slices of country or multigrain bread (1 cm thick) | 8 | 8 (about 3/8 inch thick) |
| Thick slices of Rostello ham with herbs | 4 | 4 |
| Salers or Laguiole AOP cheese | 100 g | 3.5 oz |
| Milk | 75 cl (750 ml) | About 3 cups |
| Flour | 65 g | 2.3 oz (about 1/2 cup) |
| Salt and freshly ground pepper | To taste | To taste |
Method
Step 1: Make the truffle bechamel
Melt 65 g of the black truffle Bordier butter over low heat, add the flour and whisk the two together. Cook for 2 minutes. Pour in the cold milk and cook, whisking, until the sauce thickens. Set it aside to cool. Grate the cheese and set that aside too.
Step 2: Toast and butter the bread
Toast the slices of country bread. Melt the rest of the truffle butter and brush it over 4 of the toasted slices.
Step 3: Assemble the croques
Start with an unbuttered slice. Spread it generously with bechamel, lay on a slice of Rostello ham, add a second layer of bechamel, and scatter over the grated cheese. Close each sandwich with one of the buttered slices, buttered side up.
Step 4: Bake and serve
Bake for 5 minutes in an oven preheated to 200°C, about 390°F. Serve with a salad of young shoots.
Tips from our kitchen
- Cook the bechamel down until it holds a spoon. Bordier lists 75 cl of milk against 65 g of flour, which is a loose ratio for a sauce that has to be spread rather than poured. Our guidance is to reduce it well past the point where it first thickens, or to start with about half the milk and add the rest only if it goes stiff. A runny bechamel soaks the bread and the croque collapses. This is our reading, not something the source specifies.
- Cold milk into a hot roux, all at once. The temperature difference is what prevents lumps. Add it in one go, whisk hard for the first thirty seconds, then let it come up to a simmer while you keep the whisk moving across the bottom of the pan.
- Let the sauce cool before you build. The recipe says so and it is worth obeying. Warm bechamel is slack and runs off the toast. Cooled, it is thick enough to hold its shape under the ham and the cheese.
- Toast properly, not lightly. Country bread at 1 cm needs real colour on both sides. That dried surface is the barrier between the bread and the sauce, and it is the difference between a croque you can pick up and one you eat with a fork.
- Grate the cheese, do not slice it. Salers and Laguiole are firm and dry, and slices tend to slide and pool. Grated, they melt evenly across the top in the five minutes available.
- Do not add truffle oil. It is synthetic almost without exception, and its single note flattens the real thing. If you want more truffle, use more truffle butter.
How to serve it
Bordier serves it with a salad of young shoots, which is the right call: something sharp and undressed cuts through a sandwich this rich. Dress the leaves with lemon and a little oil, nothing creamy. This is lunch rather than a starter, one croque per person, and a glass of red from the Loire or a Breton cider handles it well. If truffles are the part that interests you here, our guide to Plantin truffles covers the species, the seasons, and what is worth paying for.
Where to buy Bordier Black Truffle Butter in the US
The French Pantry ships Bordier butter across the United States in insulated overnight packaging, straight from the workshop in Brittany.
- Churned Perigord Black Truffle Butter by Bordier (4.4 oz): hand-churned Breton butter at 3.4% Tuber melanosporum, introduced in 2024.
For the rest of the flavoured butters, browse the Maison Bordier collection.
Frequently asked questions
How much Bordier truffle butter do I need?
The recipe calls for 95 g, split as 65 g for the bechamel and 30 g for brushing the toast. A Bordier block is 4.4 oz (125 g), so one block makes four croques with about 30 g left over.
Can I substitute another butter?
Not without changing the dish, because the truffle is the point. If you want a croque-monsieur with a different character, Bordier's Roscoff onion butter works in exactly the same bechamel, and we have a separate recipe for it. Plain butter plus a shaved fresh truffle is the other route, though the aroma will not survive the oven the way it does when it is held in fat.
What can I use instead of Salers or Laguiole?
Comte or a young Cantal are the closest available substitutes: firm, nutty, and mild enough to leave the truffle in front. Gruyere works too. Avoid anything sharp or blue.
How should I store the butter?
Keep it wrapped and refrigerated, and cut only what you need. Truffle aroma escapes quickly once the block is open, so press the paper firmly onto the cut face and use it within a week or two of opening for the best of it.
Does Bordier butter need refrigeration?
Yes. Bordier butter is a fresh, hand-churned product and ships cold. Refrigerate it as soon as it arrives. For this recipe it goes straight from the fridge into the pan, so there is no need to soften it.
Can I make the bechamel ahead?
Yes, and it is easier that way. It keeps two days in the fridge with a piece of parchment pressed onto the surface to stop a skin forming. Bring it back to a spreadable consistency with a whisk and a splash of milk before you build the sandwiches.
Related reading
- Plantin Truffles
- Bordier Butter: What It Is, Why Chefs Love It, and How to Use It
- How to Choose Your French Butter: A Buyer's Guide
Recipe and photograph adapted from Maison Bordier, with thanks. The French Pantry is an authorized US retailer of Bordier butter.