Heat the oven to 375°F with a rack in the middle.

Crumble the sausage into a 10-inch oven-safe skillet and cook over medium-high heat, breaking it up, until browned and cooked through, 7 to 8 minutes. Leave the fat in the pan.

Mince the garlic and stir it in for 30 seconds. Add the spinach in handfuls, stirring and pressing it down until fully wilted and any liquid has cooked off, about 3 minutes.

In a bowl, whisk the eggs, heavy cream, salt, and pepper until smooth, then stir in the cheddar.

Spread the sausage and spinach evenly across the skillet and pour the egg mixture over it. Cook on the stove without stirring for 2 minutes, until the edges begin to set.

Scatter the parmesan over the top and move the skillet to the oven. Bake 14 to 16 minutes, until the edges are puffed and the center only jiggles slightly.

Rest 5 minutes, then slice into 6 wedges and serve.