Caramelized Onion + Zucchini Egg White Casserole

A green glass casserole dish with zucchini rounds and melted cheese on a placemat.

Caramelized Onion + Zucchini Egg White Casserole

Caramelized Onion and Zucchini Egg White Casserole is a delicious savory breakfast elegant enough for company, but perfect for meal prep, too.

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Breakfast

American

173 kcal

Equipment

Ingredients

2 small zucchini, cut into ⅛-inch rounds
kosher salt + fresh cracked black pepper
5 teaspoon olive oil, divided
1 large Spanish onion, cut in half, then into thin wedges/slivers
4 cloves garlic, minced
½ teaspoon Calabrian chili paste, optional
1 teaspoon dried thyme, or 1 tbsp fresh
16 ounce liquid egg whites, 1 carton
¼ cup greek yogurt
4 ounce white cheddar, shredded off the block

Instructions

Preheat your oven to 350°F. Spritz a 8x11.5-inch (or 2 quart) casserole with cooking spray.
Spread the zucchini rounds in a single layer on a sheet pan or cutting board. Lightly sprinkle with a pinch or two of salt. Leave to sweat while you complete the next step.
Heat 3 teaspoons (1 tbsp) of olive oil in a nonstick skillet over medium heat. Once shimmering, add the onion and garlic. Season with 1/4 tsp kosher salt + several grinds of black pepper. Stir occasionally, and cook for 15 minutes. If using, stir in the calabrian chili paste, then remove the onions to the casserole dish. Sprinkle with half the cheese.
Add the remaining 2 teaspoons of olive oil to the skillet to heat. Blot the zucchini with a towel to remove the water that dots the surface, then add the zucchini and thyme to the skillet. Season pepper only, and cook for another 10 minutes so the zucchini softens and releases more of its moisture. Transfer zucchini to the casserole.
In a large bowl, whisk the egg whites + greek yogurt together for about 1 minute until foamy. Season with 1/2 tsp kosher salt + several grinds of black pepper.
Pour the egg mixture over the vegetables then sprinkle on the rest of the cheese.
Bake for 25 to 30 minutes until the eggs are set. Rest for 5 minutes. Cut into 6 portions.

Notes

A Note on Watery Vegetables: I first salt, then sauté the zucchini to draw out as much of the moisture as possible. Caramelizing the onions has the same effect. If the vegetables aren’t precooked, your casserole will be swimming in liquid. There may still be a tiny bit in the end, but not an offensive amount.

Storing + Reheating

For meal prep, I allow the casserole to cool, wrap it in plastic wrap, then pop the whole dish in the fridge. Once a couple servings have been enjoyed, I’ll transfer the rest into an airtight container.
A minute and a half in the microwave is about right for reheating a single slice.

Make Ahead Tips

Option 1: Sauté the onions/garlic and zucchini/thyme per the recipe instructions then allow to cool. Shred the cheese. Store each component in separate airtight containers in the refrigerator. Assemble the casserole while the oven preheats. (Preferred method.)
Option 2: Assemble the entire casserole ahead of time then wrap it tightly to store in the fridge. Let it sit on the counter while the oven preheats. Add a couple more minutes to the bake time if necessary so the egg whites are completely set and hot in the center (160°F).

Nutrition

make ahead, oven, stove top, vegetarian

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