Preheat oven to 375°F (190°C). If using a store-bought crust, prick the bottom with a fork a few times. If blind-baking is recommended for your crust, do so according to package directions, then let cool.

Heat olive oil in a large skillet over medium heat. Add the chopped spinach and cook until wilted, about 2-3 minutes. Remove from heat and squeeze out any excess liquid using a fine-mesh sieve or paper towels. This step is crucial to prevent a watery quiche.

In a large mixing bowl, whisk together the eggs, heavy cream, salt, pepper, and nutmeg until well combined.

Sprinkle half of the Gruyère and cheddar cheese evenly over the bottom of the prepared pie crust.

Layer the wilted spinach over the cheese, then top with the diced ham.

Sprinkle the remaining cheese over the ham and spinach.

Carefully pour the egg and cream mixture over the fillings in the pie crust.

Place the pie plate on a baking sheet (to catch any potential spills) and transfer to the preheated oven.

Bake for 45-55 minutes, or until the center is just set and the crust is golden brown. A knife inserted near the center should come out clean. If the crust edges brown too quickly, cover them loosely with foil.

Remove from oven and let the quiche rest on a wire rack for at least 10-15 minutes before slicing and serving. This allows the custard to fully set.