Directions

1. In a large skillet, melt the butter and sauté the sliced onions for 5 minutes, stirring frequently. You want the onions to brown but not burn, so cook over medium-low.
2. Add the salt, the pepper, the dried thyme, the garlic powder, and the sugar. Continue cooking for another 5 to 10 minutes until the onions are softened. If the pan starts to dry out too much or burn, add a little water as you sauté.
3. When they’re done, set them aside.
4. Lay out the bread slices and spread mayonnaise on one side of each slice.
5. To assemble each sandwich: place approximately 1 ounce of fontina, 1 ounce of cheddar, and 1.5 ounces of smoked Gruyere on one of the slices of bread.
6. Top the Gruyere with a mound of the sautéed onions, and then a second slice of bread (mayonnaise-side down).
7. Butter the top of the sandwich, then place in a skillet (butter side down) on medium heat, cook that side until browned. Butter the slice of bread that is now the top and flip it over to cook that side until browned.