8 slices La Brea Bakery Sourdough Loaf
1/4 cup whole-grain mustard
8 ounces Gruyere cheese, sliced into 24-32 1/16-inch-thick slices
1/3 cup extra-virgin olive oil
2-3 tablespoons champagne vinegar or white-wine vinegar
2 tablespoons kosher salt
1 tbs freshly cracked black pepper
2 medium yellow onions, sliced into 1/8-inch-thick slices
In a medium bowl, combine the oil, vinegar, salt, and pepper. Add the onions, toss to coat them, and allow to marinate for 15-20 minutes at room temperature. Season them with more vinegar, salt, and pepper, to taste.
TO ASSEMBLE THE SANDWICHES:
Set half of the slices of bread buttered side down. Spread an even layer of mustard over the bread and cover with half the cheese slices, folding them back in toward the middle if they extend past the edges of the bread. Scatter the marinated onions on top and place the remaining cheese slices over the onions. Put the top slices of bread over the cheese, buttered side up.
Grill the sandwiches in a moderately hot skillet until the bread is golden brown and the cheese has melted. Cut each sandwich in half on the diagonal.
Cut each sandwich in half on the diagonal.