Sourdough Discard Vegetable Skillet Frittata
A rustic Italian-American skillet frittata that puts sourdough discard to delicious use. Tangy sourdough starter creates a golden, slightly crispy base while eggs bind together sautéed zucchini, bell peppers, and caramelized onions, finished with melted Gruyère and fresh herbs. Perfect for brunch, lunch, or a simple dinner—baked until the center is just set and the edges are lightly browned.
- Prep
- 15 min
- Cook
- 20 min
- Wait
- 5 min
- Total
- 40 min
- Makes
- 1 frittata (4 servings)
Steps
Before you start
- Preheat your oven to 400°F (200°C)
- Have all vegetables prepped and ready before you start cooking
- Use active, bubbly sourdough discard at room temperature for best results
Whisk eggs and sourdough
- In a large bowl, whisk together the 8 eggs, sourdough discard, kosher salt, and black pepper until fully combined and smooth.
- The mixture should be evenly blended with no streaks of sourdough visible.
- Set aside.
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Ready when: mixture is smooth and uniform in color
Tip: Don't overmix; just ensure the ingredients are evenly distributed.
Sauté onion until softened
- Heat 2 tablespoons (30 ml) olive oil in a 10-inch (25 cm) cast-iron or oven-safe nonstick skillet over medium heat.
- Add the sliced onion and cook, stirring occasionally, for 5–6 minutes until soft and beginning to turn golden around the edges.
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Ready when: onion is soft and lightly caramelized at the edges
Tip: Stir occasionally so the onion doesn't burn but develops color evenly.
Add zucchini and bell pepper
- Stir in the zucchini and bell pepper chunks.
- Cook, stirring frequently, for 4–5 minutes until the vegetables are tender and the zucchini has lost most of its raw crunch.
- The bell pepper should still have a slight firmness.
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Ready when: zucchini is softened and bell pepper is tender-crisp
Tip: Don't overcook the vegetables—they'll continue to soften in the oven.
Add garlic and herbs
- Add the minced garlic and chopped thyme leaves.
- Stir constantly for 30 seconds until fragrant.
- The heat will toast the garlic slightly without burning it.
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Ready when: garlic is fragrant
Tip: Keep the heat at medium so the garlic doesn't burn.
Pour in egg mixture
- Pour the whisked egg and sourdough mixture evenly over the vegetables.
- Use a spatula to gently distribute the vegetables and spread the egg mixture to an even thickness.
- Let it cook undisturbed on the stovetop for 2–3 minutes until the edges begin to set and appear slightly opaque.
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Ready when: edges of frittata are opaque and starting to pull away from skillet sides
Tip: Don't stir the mixture once it begins to set; this helps a unified frittata develop.
Add cheese and bakeOven 400°F / 205°C
- Sprinkle the shredded Gruyère cheese evenly over the top of the frittata.
- Transfer the skillet to a preheated 400°F (200°C) oven and bake for 12–15 minutes until the frittata is nearly set in the center (a small wobble is okay) and the edges are light golden brown.
- The cheese should be melted and bubbling.
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Ready when: center is barely set with a very slight wobble, edges are golden brown, cheese is melted and bubbling
Tip: A slightly underdone center is better than overbaking, as carryover heat will set it further during resting.
Rest and garnish
- Remove the skillet from the oven and let it rest at room temperature for 5 minutes.
- This allows the center to finish cooking gently and makes slicing easier.
- Garnish with fresh chopped parsley if desired.
- Serve warm or at room temperature, cut into wedges directly from the skillet.
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Ready when: center is fully set and holds together when sliced
Tip: Don't skip the resting time—it prevents the frittata from being watery and makes it easier to cut clean wedges.
Good to know
Tips
- If your skillet handle isn't oven-safe, wrap it in foil before baking to prevent burning.
- Sourdough discard that's actively bubbling and alive at room temperature gives the frittata a subtle tang and lightness. Discard that's been refrigerated or inactive works but will be less flavorful.
- For a crispier bottom, place the skillet over medium-high heat for the last 1–2 minutes after you pour in the egg mixture (watch carefully so it doesn't burn).
- Serve with a simple green salad dressed in lemon vinaigrette, crusty bread, or roasted potatoes for a complete meal.
Make ahead
You can prep all vegetables and whisk the egg mixture up to 4 hours ahead, storing each separately in the refrigerator. Cook the frittata fresh when you're ready to serve.
Storage & reheating
Store leftover frittata covered in the refrigerator for up to 3 days. Reheat gently in a 300°F (150°C) oven for 10 minutes or eat cold. Do not freeze, as the egg texture becomes watery upon thawing.
Substitutions
- Gruyère cheese, coarsely shredded → sharp cheddar, Comté, or aged Gouda. Any firm, melting cheese works; use about the same weight. Gruyère adds a subtle nuttiness that pairs well with sourdough tang.
- medium zucchini → summer squash, thin asparagus spears, or broccoli florets. Choose vegetables of similar cooking time so they finish tender at the same moment.
- fresh thyme leaves → fresh sage, rosemary, or oregano. Use the same amount. Each herb brings its own character; thyme is mild, sage is earthy, and rosemary is bold.
- active sourdough starter discard → whole wheat or rye sourdough discard; or 2 tablespoons all-purpose flour mixed with 2 tablespoons whole milk if you have no starter. The sourdough adds tang and creates a slightly crispy texture. Substitutes will produce a milder, more custard-like result.
