Baking a frittata in a low oven gives a creamy, custardy texture that's a lot silkier than the usual version. This one is speckled with salmon, ricotta and chives. It's great served with leftover yogurt sauce and sliced tomatoes.
Technique tip: Take care not to overcook the frittata, it's done as soon as the top is solid, but still slightly jiggly.
Swap options: You can leave the ricotta out for a dairy-free version.
Heat oven to 300°F. Position a rack near the top of the oven.2.
In a heavy, well-seasoned cast-iron or nonstick, oven-proof skillet (preferably 8- or 9-inch), heat the butter over medium heat. Add onions and 1/4 teaspoon salt; cook until tender and browned in spots, about 7 minutes.3.
While the onion is cooking, in a large bowl, whisk eggs; stir in 1/4 teaspoon salt and 1/4 teaspoon black pepper. Add the egg mixture to the pan, stirring gently to incorporate onions. Fold in salmon. Spoon dollops of ricotta over top of frittata; sprinkle with chives. Cook until the bottom is just set, about 2 minutes.4.
Transfer the skillet to the oven; bake until eggs are set around the edges but still slightly custardy in the center, 12-15 minutes for a 9-inch skillet, 15-20 minutes for an 8-inch skillet (check frequently towards the end to avoid overcooking eggs). Slide frittata out onto a plate. Before serving, drizzle with oil and lemon, sprinkle with flaky salt and additional black pepper.