Mushroom and Caramelized Onion Frittata

By the looks of social media, it seems like most people these days do some form of meal prep (or at least try to!), and usually it involves prepping healthy work lunches for the week to avoid running out for fast food midday. With as busy as I am,  I’ve actually gotten into the habit of prepping all of my meals in advance and using the freezer to my advantage: breakfast, lunch, dinner, and snacks.

Obviously oatmeal, cereals, and granola bars make for quick breakfasts, but when you’re trying to eat a high protein, low carb diet, eggs are often a better option for breakfast. However, we all know eggs take a little bit more time in the morning, often more time than we have to give (I already wake up at 5am as it is!). That’s why egg frittatas are such a great addition to your weekly meal prep routine. They’re easy to make, will last the entire week, and you can even make a couple at a time and freeze them (they will last up to three months in the freezer!).

Now if you’re not into meal prepping, I’ve been known to make frittata’s for “breakfast for dinner” which is always a hit!

Eggs are so versatile, and there are so many amazing flavor combinations you can create in a frittata, but this mushroom and caramelized onion version is one of my favorites. It’s earthy, light, and because there’s not meat, prep is even faster (which is perfect for my busy schedule!).

I cook all of my fillings one at a time in the same saute pan. The reason I do them separately is because they all take a different amount of time to cook. I start with the caramelized onions because they take the longest. Add olive oil and butter to the pan until heated, then add your sliced onion, salt, pepper, and a dash of balsamic vinegar. If you don’t have balsamic vinegar, you can use a teaspoon of sugar. This just helps to make the onion caramelize faster.

When finished, transfer the onions to the bottom of a buttered cast iron skilet, then add the mushrooms to your saute pan. Cook until tender, and then move to the skillet with the onions. This should only take about 5 minutes.


Lastly, saute your spinach. This is fast and will only take a minute. Move the spinach to the skillet as well.


Now in a large mixing bowl, add your eggs, milk, and seasoning. I always add a little more seasoning than I think I need because a bland frittata or egg bake is the worst. Whisk well until the the eggs are frothy, then mix in your shredded cheese and stir just until combine. Pour the egg mixture into the cast iron skillet on top of your fillings, and sprinkle with red pepper flakes.


Bake at 375 degrees for 22-25 minutes until the center is set but not brown yet. The frittata will continue to cook in the hot cast iron skillet when you remove from the oven so do not overcook!

Allow the frittata to cool for 10 minutes before serving. If you plan on freezing, allow the egg to completely cool (I usually refrigerate for a couple of hours), then cut it into pieces and wrap each individually with plastic wrap. I put all of them all in a labeled freezer bag with the date. These will last for a few months in the freezer and make the perfect quick breakfast. Just take a slice out of the freezer and move to the refrigerator the night before. In the morning, microwave just until warm!

Happy meal prepping!!!


Mushroom and Caramelized Onion Frittata

  • Servings: 10-12
  • Difficulty: Easy
  • Print

1 10-12 inch cast iron skillet (or any oven safe skillet or baking dish you have)
14 large eggs
1 large yellow onion
8oz sliced baby bella mushrooms
2-3 cups fresh spinach
2 cups shredded white cheddar or Monterey Jack cheese
2 tbsp butter
2 tbsp olive oil
Dash of balsamic vinegar
Salt, Pepper, Paprika, Red Pepper Flakes

1. Coat cast iron skillet in melted butter and set to side. Preheat oven to 375 degrees.
2. Slice onion into thin strips. Put in medium sized saute pan over medium to high heat with 1 tbsp of oil and 1 tbsp of butter. Add a dash of balsamic vinegar as well as salt and pepper. Allow to saute for 15-20 minutes until very tender, stirring frequently. When finished, layer onions in bottom of buttered cast iron skillet.
3. To the same saute pan over medium heat, saute mushrooms until tender (about 5 minutes). Drain excess water/juice from pan before layering on top of onions in cast iron skillet.
4. Add spinach to saute pan and cook for just a minute until spinach is tender. Layer on top of onions and mushrooms.
5. In large bowl, crack 14 eggs. Add 1/2 cup milk (any type of dairy or nondairy milk you have). Add 2 teaspoons salt, 1 teaspoon pepper, 1 teaspoon of paprika, and 1 teaspoon of red pepper flakes. Whisk well until eggs are frothy. Add the shredded cheese and stir to combine. Pour mixture into cast iron skillet.
6. Put in 375 degree oven for 22-25 minutes until middle is set but not overcooked. The frittata will continue to cook in the skillet when you take it out of the oven so do not overcook. Allow to cool 10 minutes before serving.
**To freeze, refrigerate for a couple of hours. Slice into separate pieces and wrap individually in plastic wrap. Will last for 3 months in the freezer.

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