Preheat oven to 400°. Spray a 2-quart baking dish with cooking spray.
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 becomes translucent, 4 to 5 minutes.
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.
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.
Add 1½ cups mozzarella and 1 cup Parmesan, stirring well. Spoon into prepared dish.
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, about 10 minutes.
Notes
KITCHEN TIP Cooking spinach reduces its volume by three-quarters, so don’t be alarmed by the need for five bags of spinach for this recipe.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/creamed-spinach-2/