Ingredients
- 4 pieces thick-cut sourdough or brioche pullman bread slices
- 6 ounces aged Gruyère, freshly grated
- 2 ounces Comté, freshly grated
- 2 tablespoons black truffle butter
- 2 tablespoons unsalted European-style butter, for the pan
- 2 large yellow onions, thinly sliced
- 1 tablespoon dry sherry or white wine
- 1 teaspoon fresh thyme leaves
- 1 tablespoon crème fraîche
- 1/2 teaspoon fleur de sel
- 1/3 teaspoon freshly cracked black pepper
Steps
1
Caramelize the onions: Place a heavy-bottomed skillet over medium-low heat. Melt 2 tablespoons unsalted European-style butter, for the pan and add the 2 pieces large yellow onions, thinly sliced. Cook slowly, stirring every few minutes, allowing the onions to soften and deepen into a rich amber. After about 40 minutes 40:00, deglaze with 1 tablespoons dry sherry or white wine and stir in 1 teaspoons fresh thyme leaves. Fold in 1 tablespoons crème fraîche, season with a pinch of 1/2 teaspoon fleur de sel, and set aside.
2
Prepare the truffle butter bread: Spread 6 ounces aged Gruyère, freshly grated of truffle butter generously and evenly across one side of each of the 4 pieces thick-cut sourdough or brioche pullman bread slices. These buttered surfaces will become the golden exterior of your sandwich — don't be shy.
3
Layer the cheese: On the unbuttered side of two slices, layer a foundation of 6 ounces aged Gruyère, freshly grated Gruyère, then a generous spoonful of caramelized onions, followed by 2 ounces Comté, freshly grated Comté. Finish with a final layer of Gruyère to 'glue' the top slice in place. Season with 1/3 teaspoon freshly cracked black pepper.
4
Grill low and slow: Warm a cast-iron skillet or heavy pan over medium-low heat. Place the sandwiches butter-side down. Cover loosely with a lid or foil tent to trap heat and encourage even melting. Cook for 5–6 minutes until deeply golden on the bottom.
5
Flip and finish: Carefully flip each sandwich and press gently with a spatula. Continue cooking, uncovered, for another 4–4 1/2 minutes until the second side is equally bronzed and the cheese is fully molten and just beginning to ooze at the edges.
6
Rest and serve: Transfer to a wire rack and rest for 2 minutes. This keeps the crust crisp and lets the cheese settle. Finish with a pinch of 1/2 teaspoons fleur de sel. Slice on the diagonal and serve immediately, ideally alongside a lightly dressed frisée salad or a cup of velvety tomato bisque.
Notes
On the cheese: Always grate Gruyère and Comté fresh — pre-shredded cheese contains anti-caking agents that inhibit proper melting. A microplane or coarse box grater yields the best melt.
On the bread: Brioche delivers a richer, slightly sweet crust; sourdough offers a more complex tang that plays beautifully against the truffle. Either should be cut at least ¾-inch thick to hold the filling with integrity.
On the onions: Patience is everything here. Rushing the caramelization over high heat produces steamed onions, not the jammy, deeply sweet result this sandwich deserves. They can be made up to three days ahead and refrigerated.
Additions to elevate it even further: A combination of Dijon mustard, a swipe of fig jam, some pancetta, or slow-roasted Roma tomatoes, or a finishing drizzle of wildflower, truffle or chestnut honey can take this to an even more rarefied level.
Wine pairing: A glass of white Burgundy or an aged Comté-region Chardonnay from Jura is a sublime companion.