First things first. Heat 2 tablespoons of the olive oil in a large nonstick skillet over medium heat. Add the onion slices to the pan. Sauté them for about 10 minutes. You want them to turn translucent and lightly caramelized, releasing a sweetness that elevates our frittata.

Grab a large mixing bowl. Crack those eggs in and whisk them vigorously. You want the yolks and whites to be blended thoroughly. Throw in your flaky sea salt, pepper, and half of the oregano, mixing it until everything is well-combined.

With the onions now beautifully softened, it’s time to introduce the rest. Reduce the heat to low. Pour the egg mixture over the onions in the skillet. Gently add the ricotta dollops, Grana Padano cheese, sliced tomatoes, and basil leaves. Make sure these ingredients are evenly distributed in the egg mixture.

Now, let it cook. Keep the heat low. Cook for around 5 to 8 minutes, until the edges start to set. Use a spatula to lift the edges, allowing the uncooked egg to flow underneath. This little trick lets your frittata cook evenly.

Preheat your oven’s broiler. Once the edges are firm, transfer the skillet to the broiler. Watch it closely as it cooks for an additional 3 to 5 minutes. You're looking for a golden top, puffed but not burnt. The frittata should be set in the center.

Remove the skillet from the oven. Let the frittata sit for a few moments before cutting into it. This allows the flavors to settle and enhances the textures. Slice it up and get ready for the applause!