French Onion Soup Frittata with Emmi Kaltbach Le Gruyère | culture: the word on cheese
☰ menu   

French Onion Soup Frittata with Emmi Kaltbach Le Gruyère

Cave-aged cheeses are cool. Or at least they are for a few months.

Emmi USA’s Kaltbach™ Le Gruyère® AOP is easily recognizable, with its rustic brown rind and smooth, crumbly paste. Flavorful without overwhelming the palate, this grass-fed cow’s milk cheese is aged in one of the most unique locations in the world.

Deep under the Alpine Valley of Switzerland lies a 22 million-year-old sandstone cave. Kaltbach Cave is named for the tranquil river that runs through it; the German kaltbach literally means “cold creek.” In 1993, bi-continental cheese producer Emmi Roth purchased the cave as an aging space for their award-winning cheeses.

No one knows exactly when cheeses were first aged in caves. However, the stable humidity and naturally occurring minerals and bacteria found in caves provide the perfect place for young cheeses to develop singular nuances. In the US, more and more affineurs are turning to abandoned tunnels and other human-made structures that mimic the natural aging chambers─like Kaltbach Cave─that have been used by cheesemakers in Europe for thousands of years.

French Onion Soup Frittata with Emmi Kaltbach Le Gruyère

Emmi Roth USA
Emmi Kaltbach Le Gruyère and caramelized onions join forces in this playful twist on the well-loved soup—it’s just as cozy and comforting as the original.
Servings 6


  • 2 tablespoons olive oil
  • 2 large yellow onions thinly sliced
  • Kosher salt
  • Freshly ground black pepper
  • 8 large eggs
  • 1/3 cup whole or 2% milk
  • 4 ounces Emmi Kaltbatch Le Gruyère grated (about 1 cup) and divided
  • 1 tablespoon chopped fresh thyme leaves divided
  • 1 tablespoon sherry vinegar


  • ►Arrange a rack in the top third of the oven and heat to 350°F.
  • ►Heat the oil in a 10- to 12-inch cast iron or oven-safe nonstick skillet over medium heat. Add the onions, season with salt and pepper, and cook, stirring occasionally and scraping up any browned bits that accumulate on the bottom of the pan, until the onions are soft and deeply caramelized, about 45 minutes.
  • ►Meanwhile, whisk the eggs, milk, half the Gruyère and half the thyme together in a large bowl. Season with salt and pepper.
  • ►Once the onions are caramelized, stir in the sherry vinegar and scrape up any remaining browned bits from the bottom of the pan. Spread the onions into an even layer and pour the egg mixture over the top. Stir gently once or twice to make sure the onions are evenly distributed among the egg mixture. Sprinkle the remaining Gruyère and thyme evenly over the top. Cook undisturbed until the eggs at the edge of the pan begin to set, about 2 minutes.
  • ►Transfer the skillet to the oven and bake until eggs are just set, about 20 minutes. To check, cut a small slit in the center of the frittata. If raw eggs run into the cut, bake for another minute or two. If not, then the eggs are set. Heat the broiler to HIGH. Broil until the top of the frittata is lightly golden-brown in spots, 2 to 3 minutes. Cool in the pan for 5 minutes, then slice into wedges and serve warm.
  • Sponsored by Emmi USA.

Leave a Reply