Bring a big saucepan of water and two teaspoons of salt to a boil.
Add the spinach and cook for 1 minute, or until it is wilted.
In a sieve or colander, drain the spinach.
Rinse the spinach with cold water, then squeeze the water out of each fistful.
Cut the spinach bunches into 3/4-inch chunks.
Melt the butter with the garlic and onions in a large skillet.
Cook for 8-10 minutes on medium-low, or until the onions are transparent.
Combine the remaining kosher salt, black pepper, and freshly grated nutmeg into the skillet.
Add the flour and stir with a wooden spoon over low heat for 2-3 minutes, or until the scent is nutty.
Pour half cream into the mix and bring to a boil.
Mix in the mozzarella and cream cheese.
Cook, occasionally stirring, for 6-8 minutes, or until the mixture thickens.
Stir in the spinach and Parmesan cheese to mix.
