- 3 pounds frozen chopped spinach or fresh spinach
- 4 Tbsp. unsalted butter
- 5 Tbsp. flour
- 4 cups warm milk
- 1 tsp. kosher salt
- 1 tsp. freshly grated nutmeg
- 1 cup freshly grated Parmesan cheese
If using frozen spinach, bring 1 cup of water to a boil, and add the frozen spinach. Cover and simmer until the spinach is thawed (about 6 to 8 minutes). Drain in a wire mesh and use a wooden spoon to press as much water as you can out of the spinach.
If using fresh spinach, cook in boiling water just until wilted. Drain. Lay the spinach on a clean dish towel, and spread it out to cool for 30 minutes. Gather all the spinach in the middle of the towel, bring up the sides, and twist tightly, squeezing out as much water as you can. Transfer spinach to a bowl and break apart any clumps. It's important to squeeze out as much water as you can; if too much water is left in, the spinach will be runny and not creamy.
In a sauce pot on medium-high heat, melt the butter. Add flour and mix, forming a roux. Slowly add all of the warm milk, stirring constantly until thickened. Do not boil. The mixture will form tiny bubbles at the edges in 5 to 6 minutes. When that happens, remove from heat, add the salt and nutmeg, and mix well.
Pour the sauce over the spinach, and mix well. Add Parmesan cheese and mix well. Add more salt if necessary.
Preheat the oven to 350°F.
Pour into a baking dish or pie dish and cover tightly with foil. Bake for 30 to 40 minutes.