Step 1

Preheat the oven to 325°F, and set an oven rack in the middle position.

Step 2

Heat the oil in a 10-inch ovenproof nonstick skillet over medium heat. Add the shallots and cook, stirring frequently, until softened, 3 to 4 minutes. Do not brown. Add half of the spinach and cook until wilted down, about 1 minute. Add the remaining spinach and 1/4 teaspoon of the salt and continue cooking until all of the spinach is wilted, 1 to 2 minutes more.

Step 3

In a large bowl, whisk together the eggs, heavy cream, pepper, and the remaining 1/4 teaspoon of salt.

Step 4

Add the cooked spinach mixture, Cheddar, Parmigiano Reggiano, and basil to the egg mixture and stir to combine. Pour the mixture back into the pan (no need to wash it), then place it in the oven and bake until set, 20 to 23 minutes. Immediately place an oven mitt over the pan handle to remind yourself that it is hot (it's easy to forget and burn your hand, and the handle stays hot for a long time). Serve the frittata directly from the pan, or use a rubber spatula to loosen the edges and slide the frittata onto a serving platter.

Step 5

Freezer-Friendly Instructions: The cooked frittata can be frozen for up to 3 months. Remove the frittata from the freezer about 24 hours prior to serving and reheat it in the microwave or, covered with foil, in a 300°F oven until hot in the center.