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 gruyere 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 of 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 in another onion instead and proceed with the recipe as directed.
You can also use just about any cheese you like instead of gruyere, though keep in mind that some are more strongly flavored and so less should be used, and others may not melt as well. Cheddar would be a good, cheaper substitute for the gruyere; 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’ll find it hard to fit them all in at once, so just add in 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 turning translucent by this stage.
Reduce the heat to low and continue to cook, stirring every now and then, for 30 minutes. The onions and leeks will begin turning a golden color and they will smell really good by this point. If you feel this is taking too long, and the onions and leeks aren’t yet golden, you can adjust the heat up a little. Just remember that this is supposed to take a while. If the heat is too high you will not get caramelization; instead you will get crispy onions and leeks or, worse, burnt ones.
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. You may see some brown bits stuck to the bottom of the pan. This is called a ‘fond’ and it’s full of flavor. When this happens, add a little water to the pan—about a tablespoon at a time. Scrape up the brown bits and stir well so that the flavor gets incorporated into the rest of the mixture. Repeat this as often as required until the onions and leeks are caramelized to your liking. I like them to be a medium brown and kind of jammy. At this point, taste and add a little more salt if desired.
When the onion and leek mixture is done, you can store 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 175 degrees Celsius.
In a large bowl, beat the eggs, cream, salt, pepper, and nutmeg just until combined. Stir in 1 cup of the gruyere 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.
Sprinkle the remaining 1/4 cup of gruyere 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
Caramelized Onion and Leek
- 2 onions finely sliced
- 2 leeks well cleaned, white and light green parts finely sliced
- 3 tablespoons butter
- salt to taste
- 12 large eggs
- 1/2 cup heavy cream
- 1/2 teaspoon salt
- 1/4 teaspoon pepper
- 1 pinch ground nutmeg
- 1 1/4 cups grated gruyere cheese divided
- 3 tablespoons fresh parsley or chives, or a mixture finely chopped
- 1 tablespoon extra virgin olive oil
Caramelized Onion and Leek
- In a large skillet over medium heat, melt the butter. As soon as it's foaming, start adding the sliced onion and leek, a large handful at a time. Add more once the current contents have started to shrink down a bit, stirring with every addition. Once all the onion and leek is in the skillet, add a pinch of salt.
- Cook, stirring every minute or so, until the onions are translucent, about 10 minutes.
- Reduce heat to low and continue to cook, stirring every now and then, for 30 minutes. The onions and leeks should be a golden brown by now, but still soft and not crispy.
- 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. Add water, about a tablespoon at a time, if the pan seems too dry, and stir it in. Taste and add more salt if required, then remove from heat.
- Preheat oven to 350°F (175°C).
- In a large bowl, whisk together the eggs, cream, salt, pepper, and nutmeg until well combined. stir in 1 cup of the gruyere 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 gruyere 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 cook for about 10 minutes before slicing and serving.
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