Caramelized Leek and Onion Frittata

A frittata is commonly thought of as Italy’s version of an omelet and is a great way to use up vegetables languishing in the fridge, so it can be rather simple. But it can also be quite fancy, depending on what you put in it. This caramelized leek and onion frittata with Gruyère cheese is somewhere in between.

How to Serve Caramelized Leek and Onion Frittata

Traditionally, this is a breakfast food. However, I find it also makes a great lunch or dinner, accompanied by a simple side salad and maybe some good bread.

Additions and Substitutions

If you don’t want to use leeks or can’t find them, you can just add another onion instead and proceed with the recipe as directed.

You can also use just about any cheese you like instead of Gruyère, though keep in mind that some are more strongly flavored so less should be used, and others may not melt as well. Cheddar would be a good, cheaper substitute for the Gruyère; it will taste different but will otherwise perform the same way.

Making Ahead and Leftovers

You can make the caramelized leek and onion mixture up to a few days ahead and store in the fridge until needed.

The frittata itself can be refrigerated and, when lightly reheated in the microwave, tastes almost as good as when made fresh. I have also frozen individual slices, though I find the texture toughens a little once reheated.

How to Make Caramelized Leek and Onion Frittata

Caramelize Leek and Onion

First I’ll point out to anyone who is unfamiliar with leeks that they tend to be very dirty. To clean them properly, I first trim off the dark green tops and the root end, if attached, and then cut them lengthwise, so I can clean between every layer. Then I slice and proceed with the recipe.

Take a large skillet and set it over medium heat. Add the butter and, once it has melted and starts to foam, start adding the onions and leeks. You may find it hard to fit them all in at once, so just add them about a handful at a time, stirring with each addition. You can add more once the contents of the pan shrinks down a little.

Once all the onions and leeks are in the skillet, sprinkle with a little salt and cook for about 10 minutes, stirring every minute or so. The onions should be softening and turning translucent by this stage.

Reduce the heat to medium-low and continue to cook, stirring every now and then. Each time you stir, make sure you spread the mixture over the bottom of the pan so it has as much contact as possible. If you see brown bits beginning to form on the bottom of the pan, add a little water and use it to scrap them back into the mixture. If this is happening too often and you’re worried the mixture is at risk of burning, you can reduce the heat a little. Keep cooking until the onions and leeks are very soft and beginning to turn golden; this will take around 30 minutes. Adjust the heat level as needed; remember that higher heat will yield faster results but also a higher chance of burning.

Continue to cook for another 10 minutes or until the mixture starts to darken. You’ll have to watch more carefully and probably stir more often now to ensure the onions don’t burn. Continue cooking until the onions and leeks are caramelized to your liking. This may take longer than 10 minutes, depending on your preferences. Taste and add a little more salt if desired.

When the onion and leek mixture is done, you can store it in an airtight container in the fridge for a few days before using, if that works better for you.

Preheat Oven and Make Egg Mixture

Start the oven preheating to 350 degrees Fahrenheit, or about 180 degrees Celsius.

In a large bowl, beat the eggs, cream, salt, pepper, and nutmeg just until combined. Stir in 1 cup of the Gruyère cheese and the fresh herbs.

Start on Stove

Set a 10-inch cast iron skillet over medium heat and add 1 tablespoon of oil. Once it’s hot, add half the onion and leek mixture, spreading out as evenly as you can. Pour over half the egg mixture, then follow with the rest of the onions and leeks and the rest of the egg mixture on top of that. I find that layering the ingredients this way makes for a better distribution of ingredients; if you put all the onions and leeks in first then they tend to stay on the bottom of the frittata.

Cook on the stove for about five minutes, just until the edges of the frittata are starting to pull away from the pan.

Bake

Sprinkle the remaining 1/4 cup of Gruyère cheese on top of the frittata, then carefully transfer to the oven. Your cooking time may vary and it’s important not to overcook, so I recommend checking for doneness at around the 18 minute mark. To check if the frittata is done, give the pan a little shake; the frittata should jiggle slightly when ready.

Once removed from the oven, allow the frittata to cook for about 10 minutes before slicing and serving.

Caramelized Leek and Onion Frittata

Filled with sweet caramelized onions and leeks and creamy Gruyère cheese, this frittata is a bit fancy but still easy to prepare, if you have a little patience.
Prep Time 20 minutes
Cook Time 1 hour 30 minutes
Total Time 1 hour 50 minutes
Servings 6

Ingredients

Caramelized Onion and Leek

  • 2 large onions finely sliced
  • 2 leeks well cleaned, white and light green parts finely sliced
  • 3 tablespoons butter
  • Salt to taste

Frittata

  • 12 large eggs
  • 1/2 cup heavy cream
  • 3/4 teaspoon salt
  • 1/4 teaspoon pepper
  • 1 pinch ground nutmeg
  • 1 1/4 cups grated Gruyère cheese divided
  • 3 tablespoons fresh parsley or chives, or a mixture finely chopped
  • 1 tablespoon extra virgin olive oil

Instructions

Caramelized Onion and Leek

  • In a large skillet over medium heat, melt the butter. As soon as it's foaming, add the sliced onion and leek, as well as a pinch of salt.
  • Cook, stirring every minute or so, until the onions start to soften and turn translucent, about 10 minutes.
  • Reduce heat to medium-low and continue to cook, stirring every now and then. If brown bits are forming on the bottom of your pan, add a little water and use it to scrape them off and stir them into the mixture. If this is happening too often and you're worried your onions will burn, you can reduce the heat a little. Keep cooking, adjusting the heat level as needed, until the onions and leeks are soft and beginning to turn golden, which will take around 30 minutes.
  • Continue to cook for another 10 minutes or until the mixture starts to darken. Watch carefully at this point to make sure the mixture does not burn, stirring as needed. The onions and leeks are done when they reach your preferred level of caramelization, so this may take a bit longer if you like them darker. Taste and add more salt if required, then remove from heat.

Frittata

  • Preheat oven to 350°F (180°C).
  • In a large bowl, whisk together the eggs, cream, salt, pepper, and nutmeg until well combined. Stir in 1 cup of the Gruyère and the fresh herbs.
  • Set a 10-inch cast iron skillet over medium heat and add the olive oil. When hot, add half the onion and leek mixture; try to spread it out evenly. Pour in half the egg mixture, then add the rest of the onion and leek mixture and the rest of the eggs on top of that. Cook for about 5 minutes until the frittata is starting to pull away from the edges of the pan.
  • Sprinkle the remaining 1/4 cup Gruyère on top of the frittata. Transfer to oven and bake for 18-25 minutes. The frittata is done when the middle still has a slight wobble to it. Allow to cool for about 10 minutes before slicing and serving.

Did you make this recipe? If so, follow @theflavorvortex on Instagram and post a picture using #theflavorvortex as I would love to see it!

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