Balsamic Onion & Feta Frittata (Oven Baked)

 4.6 from 11 reviews

One piece of Caramelised Onion & Feta Frittata from a tray, on a black plate with a fork, top down view.

Are you ready for the best tasting frittata you’ve ever had?

It’s a bold claim, but I have the goods to back it up. Not only does this frittata taste amazing, it’ll create 6 meals in about 35 minutes.

Let me give you some tips…

When you’re making a frittata, all of the filling veggies should be cooked before you bake in the oven.

With this particular recipe you can bake the eggplant whilst you’re caramelising the onions. Both take about 15 minutes. I like to bake the eggplant instead of frying it to save on needing to use any olive oil.

Once both of those are done you can very briefly wilt the spinach in the warm pan, before adding all of it to the eggs.

If you want to go the full monty with fully caramelised onions, I have a recipe here: How to Caramelise Onions (No Sugar).

Check out the recipe below and use the comments if you have any questions, or if you tried it and made in your own in some way.

One piece of Caramelised Onion & Feta Frittata from a tray, on a black plate with a fork
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One piece of frittata from a tray, on a black plate with a fork

Caramelised Onion & Feta Frittata

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4.6 from 11 reviews

An amazing lunch or breakfast that will make 6 portions, all in around 35 minutes.

  • Total Time: 40 minutes
  • Yield: 6 1x


Units Scale

Caramelised Onions

  • 3 onions
  • 1/4 tsp salt
  • 2 tbsp olive oil


  • 1 eggplant (cut into cubes)
  • 12 eggs
  • 3 1/2 ozs oat milk (or dairy if you prefer)
  • 1/2 tsp salt
  • 1/8 tsp black pepper
  • 5 ozs spinach
  • 7 ozs feta


Caramelised Onions

  1. NB. For best time efficiency, caramelise the onions whilst the eggplant is in the oven (see below).
  2. Heat a pan to a medium / high heat and add the olive oil.
  3. Slice the onions and add them to the pan.
  4. Sprinkle the 1/4 tsp salt over them and keep them moving for 10 to 15 minutes, until they are a deep brown.


  1. Preheat oven to 200C / 400F.
  2. Line a baking tray with baking paper and arrange the eggplant cubes in a single layer. Bake these at 200c / 400F for 10 to 15 mins, whilst you caramelise the onions. If you want the eggplant a little more soft, bake them for 25 minutes, turning a couple of times to make sure they don't burn, since you're not using oil.
  3. Whisk the eggs, milk, salt & black pepper.
  4. Cut the feta into cubes and add to the eggs.
  5. Once the onions are done, add them to the eggs. Use the warm pan on a low heat to slightly wilt the spinach. Add the spinach to the eggs.
  6. Take the eggplant out of the oven and add to the eggs. Leave the oven on.
  7. Line a baking pan with some baking parchment and pour the frittata mixture into it. I used a baking tin 14 inch (35cm) long, by 7.5 inch (19cm) wide and 1.5 inch (4cm) high.
  8. Place the whole thing into the oven at 200C / 400F for 20 to 25 minutes.
  9. Serve immediately, either on its own, with a little hot sauce, or with a green salad or a few boiled new potatoes.
  • Prep Time: 5 minutes
  • Cook Time: 35 minutes
  • Category: Breakfast, lunch
  • Cuisine: vegetarian


  • Calories: 310
  • Sugar: 8
  • Sodium: 815
  • Fat: 21
  • Saturated Fat: 8
  • Carbohydrates: 14
  • Fiber: 4
  • Protein: 18
  • Cholesterol: 357

Related: The 10 Proven Health Benefits of Eating Eggs

One piece of frittata from a tray, on a black plate with a fork

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