Preheat the oven: Set it to 375°F (190°C). A consistent oven temperature helps the frittata set without drying out.

Whisk the egg mixture: In a bowl, whisk eggs with ricotta and milk until smooth. Season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Stir in the grated Parmesan and herbs.

Prep the pan: Heat olive oil or butter in an oven-safe skillet over medium heat. Make sure the fat coats the bottom and sides to prevent sticking.

Sauté the aromatics: Add onion and bell pepper. Cook 3–4 minutes until softened. Stir in garlic for 30 seconds until fragrant.

Add the veggies: Toss in zucchini and a pinch of salt. Cook 3–4 minutes to release some moisture. Add spinach and cook until just wilted. If using cherry tomatoes, fold in half of them now.

Combine with eggs: Lower the heat. Spread the vegetables evenly in the skillet. Pour the egg-ricotta mixture over the top, tilting the pan to distribute. Don’t stir once the eggs are in.

Start on the stovetop: Cook on low for 2–3 minutes, just until the edges begin to set. This jump-starts the cooking and keeps the center custardy.

Bake: Transfer the skillet to the oven. Bake 12–16 minutes, until the center is just set and a knife inserted near the middle comes out mostly clean. The top should look puffed and lightly golden.

Finish and rest: If you saved some tomatoes, scatter them on top for a fresh pop. Let the frittata rest for 5 minutes before slicing so it firms up and slices cleanly.

Serve: Garnish with extra herbs and a sprinkle of Parmesan. Cut into wedges and enjoy warm, room temp, or chilled.