3 tablespoons unsalted butter, plus additional for coating
½ cup all-purpose flour
2 1/2 cups whole milk
¼ teaspoon freshly grated nutmeg
Freshly ground pepper
1 tablespoon olive oil
1 small onion, finely chopped
1 clove garlic, chopped
1 pound spinach leaves, cleaned and trimmed
1 egg yolk
2/3 cup Parmesan cheese, plus additional for sprinkling
Small piece fresh mozzarella, cut lengthwise into ½ slices
For the Parmesan sauce:
½ cup heavy cream
¼ cup whole milk
¼ teaspoon ground nutmeg
2/3 cup grated Parmesan cheese
Extra virgin olive oil
Preheat the oven to 350 degrees Fahrenheit. Butter the ramekins and place in a larger baking dish. Set the aside for later.
In a small saucepan, melt the 3 tablespoons of butter over low heat. Add the flour and stir until incorporated. Continue to cook until the flour begins to thicken a bit, about 2 minutes. Gradually whisk in the milk until smooth. Cook, whisking occasionally, until the sauce has thickened slightly, about 5 minutes. Remove from the heat and stir in the nutmeg. Season to taste with salt and pepper. Transfer to a small bowl and press plastic wrap directly onto the surface to prevent a skin from forming. Allow to cool slightly.
Heat the olive oil n a large sauté pan over medium heat. Add the onion and the garlic and cook until the onion is softened, about 5 minutes. Add in the spinach and sauté until wilted, about a minute or two. Remove from the heat. Transfer the spinach to a food processor or blender and process until smooth.
In a large bowl, lightly beat the 2 eggs and egg yolk. Stir in the white sauce, pureed spinach mixture, 2/3 cup Parmesan cheese and 1 teaspoon salt. Stir until very smooth.
Pour the filling into the prepared ramekins until about 1/3 full. Add 1 slice of mozzarella and top with additional filling until about 2/3 full. Sprinkle with additional Parmesan cheese. Return the ramekins to the larger baking dish and carefully pour enough hot water into the baking dish to reach about halfway up the sides of the ramekin. Place the baking dish on the lower rack in the oven and bake until the sformati are set, about 40 or 50 minutes. The sformati are finished when a toothpick inserted into the center comes out clean. Remove from oven.
Make the Parmesan sauce: In a small saucepan, combine the cream and the milk. Bring to a boil over medium low heat. Add the nutmeg and whisk until incorporated. Remove from the heat. Stir in the Parmesan. Season to taste with salt and pepper.
Allow the sformati to rest for about 5 minutes. Run a knife around the edge of the sformati. Carefully invert or unmold onto a small plate. Drizzle or surround with the Parmesan sauce. Drizzle with your best extra virgin olive oil and serve!