4 tablespoons unsalted butter, divided
4 cups sliced sweet onions (about 2 pounds)
2 tablespoons dry sherry
1/2 cup unsalted beef stock, preferably homemade
1 sprig fresh thyme, leaves stripped from the stem
1 cup grated Gruyere cheese
4 thick slices French or Italian bread
Kosher salt and pepper, to taste
Melt 2 tablespoons of the butter in a large skillet over medium heat. Add the onions and a pinch of salt, and cook, stirring occasionally, until the onions start to turn light golden, about 10-15 minutes. Continue to cook without stirring, until a brown crust starts to form. Add a splash of water and stir, scraping the fond from the bottom, and until the water evaporates. Repeat this two or three times, until the onions are golden brown and very tender.
Pour the sherry into the pan with the onions and continue cooking until it has completely evaporated. Add the beef stock and thyme to the skillet. Increase the heat to medium-high and cook until the stock has reduced by half, about 3-5 minutes. Season generously with salt and pepper.
Heat a griddle or nonstick skillet on medium heat. Spread the remaining 2 tablespoons of butter on one side of each bread slice. Place two pieces of bread, butter side down, on the skillet. Add a handful of gruyere, followed by a generous heap of onion mixture (it can be a little messy, in a good way). Top with the remaining bread slices, butter side up, and cook, flipping once, until cheese is melted and each side is golden brown.
Makes 2 sandwiches.
Uploaded: Mar 22, 2014