FRESH SPINACH GRATIN WITH PARMESAN AND BLUE CHEESES

Steps:

• Butter 10- to 12-cup shallow baking dish. Melt 1 1/2 tablespoons butter in heavy large pot over high heat. Add 1 package spinach. Toss until wilted but still bright green, about 2 minutes longer. Transfer to colander set over large bowl. Repeat with 1 1/2 tablespoons butter and remaining spinach. Turn all spinach in colander, pressing to release all liquid. Melt 4 tablespoons of butter in same heavy large pot over medium heat. Add onions; saute until beginning to soften, about 10 minutes. Mix in flour and nutmeg. Stir 2 minutes to cook flour (do not brown.) Whisk in milk and cream. Cook until sauce thickens and boils, whisking often, about 5 minutes. Mix in 1/2 cup of Parmesan, salt, and pepper. Mix in Spinach. Transfer to dish. Sprinkle with remaining Parmesan and Blue Cheese. (Can be made 6 hours ahead. Cover; chill.) Preheat oven to 425 F. Bake gratin until bubbling and brown on top, about 20 minutes (or 25 minutes if refrigerated).