Warm Gruyere Sandwich with Mustard and Thyme

 

6 1/2-inch thick slices of levain or sourdough bread

Unsalted butter, melted

Good-quality French mustard

Fresh thyme leaves

Grated Gruyere cheese

Sea salt (optional)

 

Preheat the broiler. Place the bread slices on a baking sheet and toast one side under the broiler until golden brown. Remove from the oven and turn the slices over. Brush the melted butter on each untoasted side. Then spread with mustard and sprinkle with the thyme leaves. Sprinkle the cheese evenly over the bread. Sprinkle with salt, if desired. Broil until the edges of the bread are golden brown and the cheese is melted, about 1 minute. Remove the bread slices from the oven and serve them immediately.