When I was in college, I thought French Onion Soup was pure luxury. That may have been because I lived in a very small town at the time, or perhaps because caramelized onions, gruyere cheese, and well-browned croutons are delicious and feel inherently fancy. Gruyere, at least, has the price tag to prove it. This classic and an extra saucy order of Strawberries Romanoff were my meal of choice at a local chain every time I went to Dallas for solo dinner & a movie during those years. It always hit the spot and felt like a treat.

(For those of you wondering what kind of college student drives an hour each way to get chain restaurant soup and see movies by herself, know that I was 85 years old at birth. Thirty six years later, I am still 85 years old.)

While things have changed since college—you won’t find me eating at many chain restaurants and I live in the largest city in my country of origin—I still dig French Onion Soup. I’ve made Julia Child’s recipe several times and it’s pretty perfect, and there are many good versions around NYC too. It’s simple food, made of caramelized onions, herbs, beef stock and cognac, and finished off with a crouton and some blistered gruyere cheese. It’s so good!

All that said, may I suggest that you leave the soup for another day and make French Onion Grilled Cheese instead? Think about it: herby caramelized onions and gruyere stacked on buttered sourdough and then seared to golden brown, crunchy, cheesy perfection. I mean, what’s not to love?!

The most time consuming step of this whole recipe is caramelizing the onions. Some cooks will tell you that you can do this in 15 minutes over medium-high heat, but they are wrong. What they’re doing is sautéing, which is a great technique, but that’s not what we’re after in our French Onion Grilled Cheeses. Nope! We’re going the low and slow route, watching the onions collapse and then take on color as their natural sugars are drawn out little by little. This will take anywhere from 45-75 minutes, but I assure you it will be worth the investment.

Yes, caramelizing onions takes time, but it’s easy as can be. I frequently put a pan on the back burner while I’m working on another dish, occasionally reaching over and giving them a stir until they are browned to my preference. While caramelized onions need no help to be delicious, I like to add some French Onion flavor here so I finish them off with thyme, dijon mustard, beef (or vegetable) stock, salt & pepper. I don’t drink, so I leave the cognac out of the equation, but feel free to add a splash to the mix.

Once finished, you can use your onions right away or cover and refrigerate for later. I like to think of this as having French Onion Grilled Cheese on demand.

As for the sandwiching, it’s Grilled Cheese 101. Low heat, lots of butter, and time (about 8 minutes) are all that stand between you and crispy, cheesy, savory French Onion perfection. Pure luxury, indeed.

French Onion Grilled Cheese
makes 4 sandwiches

For the Onions:
2 tablespoons olive oil
3 medium Spanish or white onions, 1/2-inch thick half moons
Kosher or sea salt, to taste
1 tablespoon chopped fresh thyme leaves (or 1 teaspoon dried)
1/2 teaspoon dijon or grainy mustard
1/4 cup beef or vegetable stock
freshly-cracked black pepper, to taste

For the Sandwiches:
8 slices sourdough
dijon or grainy mustard
8 ounces gruyere cheese, shredded
4 tablespoons butter, softened to room temperature
few pinches of Kosher or sea salt, as needed

Make the onions. Heat olive oil in a large, heavy-bottomed pan over medium-low heat. Add onions and a pinch of salt. Cook, stirring frequently, until soft and deeply caramelized; this will take 45-75 minutes. Do not rush this step.

When onions are caramelized, stir in thyme, mustard, and stock, stirring until incorporated, but not soupy. Taste for seasoning and add salt and pepper to taste. Remove from heat. At this point, you may either use the onions immediately or cover and refrigerate for up to 4 days.

Lay all slices of bread on a surface. Spread four of the slices with mustard. Top mustard slices with ~2 tablespoons caramelized onions each, spreading to cover. Sprinkle each one with 1/4 of the gruyere. Top cheese with plain slices of bread, “closing” the sandwiches. Use a knife to spread 1/2 tablespoon softened butter on both sides of each sandwich (1 tablespoon butter per sandwich). Sprinkle butter with salt if using unsalted butter.

Heat a medium-large heavy-bottomed skillet over medium-low heat. Add sandwiches buttered-bread-side-down. Let sandwiches cook, without moving or squishing, until they are golden on the bottom, about 3-4 minutes. Flip sandwiches and let cook, without moving or squishing, until they are golden on the other side, about 3 more minutes.

Remove to plates and serve immediately.