Ingredients:
- ¾ cup (1 ½ sticks) unsalted butter, melted
- ¼ pound Gruyère, grated, plus more for dusting the ramekins
- ¼ cup all-purpose flour
- 1 ½ cups milk
- 4 large eggs separated
- 6 ounces fresh spinach, washed, steamed, squeezed dry, and finely chopped
- 1/8 teaspoon freshly grated nutmeg
- Kosher salt and freshly ground black pepper to taste
- Preheat the oven to 375 degrees with a baking sheet on a rack in the middle of the oven
- Brush the insides of six 8-ounce ramekins with a little of the melted butter followed by a dusting of Gruyère
- Put the remaining melted butter in a medium saucepan over medium heat
- When it foams, reduce the heat and gradually add the flour, stirring until there is no trace of flour left in the mixture, about 3 minutes
- Whisk in the milk in a thin stream and cook, stirring until the mixture thickens to the consistency of a heavy cream
- Turn off the heat and whisk in the egg yolks until incorporated
- Stir in the spinach and ¼ pound Gruyère and season with the nutmeg, and salt and pepper. Set aside
- Beat the egg whites in a clean bowl with an electric mixer until stiff but not dry
- Stir one quarter of the egg whites into the spinach mixture to lighten it
- Fold the remaining egg whites into the spinach mixture
- Divide the mixture evenly among the ramekins, filling them to just below the rim
- Run your finger around the inside rim of each ramekin to make a groove in the mixture
- Bake about 20 to 25 minutes, until risen and golden brown on top. Serve immediately