In a medium skillet, melt 1 tablespoon of butter over medium heat. Add the finely chopped onions along with a sprinkle of sea salt. Cook until the onions reach soft, caramelized perfection, about 10-15 minutes. This is crucial—taking the time here creates a flavor bomb for your sandwich.

While the onions are cooking, combine mayonnaise, minced garlic, Dijon mustard, and a pinch of black pepper in a small bowl.

This spread will serve as the secret weapon for flavor and to help in achieving a crispy crust. Set it aside.

Lay out your slices of bread. Spread a generous layer of your unique mixture on one side of each slice.

On the non-spread side, layer the Gruyère, followed by the cooked onions, then the cheddar and Muenster cheese—because when it comes to cheese, there's no such thing as too much. Sprinkle the minced herbs over the cheese layers.

In the same skillet, melt 1 tablespoon of butter and drizzle olive oil. This combination gives flavor and allows for even browning. Place your loaded sandwich in the skillet, cooking over medium heat. Cook for about 3-4 minutes.

You want the bread to turn golden brown before flipping. Have faith—this is going to be mouthwatering.

Now, it’s time to flip that beauty! Gently press down with a spatula to encourage melting. Cook for another 3-4 minutes on this side. If the cheese isn’t quite melting, lower the heat and cover the skillet with a lid for a minute. That helps the cheese along nicely.

Once both sides are grilled to perfection, take the sandwich out of the skillet. Let it rest for a minute, then slice it diagonally. For a finishing touch, sprinkle with bits of fresh rosemary and thyme—it’s about that presentation.