Yield: 8 to 10 servings
2 tablespoons extra-virgin olive oil
2 tablespoons unsalted butter
1 cup chopped yellow onion
2 garlic cloves, chopped
5 (9-ounce) bags fresh spinach
½ cup all-purpose flour
½ cup heavy whipping cream
2 teaspoons salt
2 cups shredded mozzarella cheese, divided
1½ cups grated Parmesan cheese, divided
1. Preheat oven to 400°. Spray a 2-quart baking dish with nonstick cooking spray.
2. In a large nonstick skillet, combine olive oil and butter. Cook over medium heat until butter has melted. Add onion and garlic. Cook until onion begins to be translucent, 4 to 5 minutes.
3. Increase heat to medium-high. Working in batches, add spinach to pan. Cook, stirring often, until spinach has wilted, 3 to 4 minutes per batch. Repeat process with remaining spinach, cooking until all spinach is wilted, stirring often. Cook for 3 to 4 additional minutes to reduce liquid, stirring often.
4. Sift flour over spinach, stirring to combine. Cook until thickened, 2 to 3 minutes. Add cream and salt, stirring well. Cook until thickened, 2 to 3 minutes. Remove from heat.
5. Add 1½ cups mozzarella and 1 cup Parmesan, stirring well. Spoon into prepared dish.
6. Cover, and bake for 15 minutes. Remove cover, and spread remaining ½ cup mozzarella and remaining ½ cup Parmesan over top. Bake until cheese is golden brown, approximately 10 minutes.