1. Preheat the oven to 400°F.

Make the Base:

1. Whisk together the eggs, cream, and ½ teaspoon salt in a large bowl. Set aside.
2. In a cast-iron skillet measuring 10 or 12 inches, heat the olive oil over medium heat. Incorporate the onion along with the remaining ½ teaspoon salt. Sauté, stirring often, until the onions become translucent, which should take about 5 minutes.
3. Add the garlic and sauté for 1 minute.

Cook the Add-ins:

1. Incorporate any additional chopped vegetables into the skillet. Cook while stirring occasionally until the vegetables are crisp-tender, which should take about 5 to 8 minutes depending on the types of vegetables used.
2. Add in the leafy greens and black pepper. Cook for 1 to 2 minutes, just until the greens are wilted.
3. Evenly distribute the vegetables across the bottom of the skillet. If the pan appears dry or the vegetables are sticking, drizzle in another tablespoon of oil. Sprinkle 1 cup of cheese over the vegetables.

Assemble and Bake:

1. Pour the egg mixture over the cooked vegetables. Tilt and swirl the skillet to ensure even distribution of the egg mixture if necessary. Top with the remaining ½ cup of cheese. Cook until the edges begin to set, which should take about 5 minutes. Then, transfer the skillet to the oven.
2. Bake for 8 to 12 minutes or until slightly puffed and the center is fully set. (A knife inserted into the center should come out clean.) Add extra cheese on top and garnish with pepper and herbs if desired. Allow to cool for a few minutes before slicing and serving.