Ingredients
Makes 2 sandwiches
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
Preparation
