The Chef-Approved Cheese To Put On French Onion Soup

French onion soup is hearty and will fill your bowl with goodness — caramelized onions and savory broth topped with bread and ooey, gooey, melty cheese. That melty magic might just be the dish's crowning glory, but recipes and opinions vary on what kind of cheese to put on French onion soup. So, we tracked down an expert to help us get it just right. Chef Miguel Pelaez Diaz talked to Mashed and let us in on a few secrets about how New York City's Smith & Mills restaurant perfects French onion soup. He also answered a pressing question: What's the best cheese to put on top?

"The cheese that we use at Smith & Mills is Gruyere," Diaz tells us. "It's the best because it browns faster than other cheeses." It's semi-hard and not only fantastic for melting but also a delicious choice for a charcuterie board.

And what does Gruyere taste like? You'll come across a wide variety of descriptions, because the flavor varies widely with age. Younger Gruyere can have grassy, earthy undertones. As it ages, it develops a nutty, sharp flavor. It tends to be a bit salty and sweet. Diaz amps up the saltiness by adding a little Parmesan cheese to the Gruyere for his French onion soup.

Perfecting the cheese topping

Chef Miguel Pelaez Diaz also shares his method to achieve that perfect amount of meltiness without burning the cheese when it's time to top your French onion soup with Gruyere. Rest a toasted piece of bread on the soup, add grated Gruyere, and place the bowl under a broiler for 2 minutes. Then, using a Microplane cheese grater, add some fine, fluffy strands of Parmesan over the melting Gruyere and broil for another 2 minutes to fully melt the Parmesan and get the cheeses nicely browned and bubbly. Then comes Diaz's melty finale: "Finish it off with a torch, if desired!"

If you're looking for an alternative to Gruyere, Diaz shares a few tips. He recommends Comte as a good option. Although he notes it's difficult to find, he says, "It adds a different flavor profile to the soup, giving it a lovely touch of nuttiness."

Diaz cautions against using very creamy cheeses. Instead, go for a semi-cured cheese like Swiss as a base layer. He explains that if you only use a hard, cured cheese like Parmesan, it might dry out too much under the broiler's high heat. The semi-cured cheese stays nice and melty, while the Parmesan on top adds a lovely crunch and that appetizing golden-brown hue. To add even more color and texture, Diaz tells us that they add chives and fried shallots to the French onion soup at Smith & Mills. Great taste, color, and texture all in one bowl!