- 1 onion
- 1 sprig fresh thyme (or a pinch dry thyme)
- Salt and pepper
- 2 slices white bread
- 1 Tablespoon unsalted butter
- 1 Tablespoon mayonnaise
- 2 slices Gruyere cheese
Melt 2 tablespoons butter in a skillet over medium-high heat. Add the sliced onions, thyme and a pinch of salt and pepper. Cook, stirring occasionally, until the onions soften and brown, about 5 minutes. Remove the onions and set aside in a bowl.
Put 1 slice over slice of bread, spoon onions on top. Cover with second slice of cheese and sadnwich with second slice of bread.
Preheat a skillet, and melt 1 tablespoon butter over medium-low heat.
Spread or brush the outside of the sandwich with 1 tablespoon mayo and cook until light golden brown, about 4-6 minutes. Flip the sandwich, (add more butter to the pan if needed) and cook the other side until brown and the cheese is melted, another 4-6 minutes. You can press down on the sandwich gently so it brown evenly, but don’t smash it.