- 2 TBS extra-virgin olive oil
- 2 TBS unsalted butter
- 1 cup yellow onion, chopped
- 2 garlic cloves, chopped
- 5 (9 oz.) bags fresh spinach
- 1/2 cup all purpose flour
- 1 cup heavy whipping cream
- 2 tsp. salt
- 2 cups shredded mozzarella cheese, divided
- 1 cup grated Parmesan cheese, divided
- 1/2 cup shredded Asiago cheese
Preheat oven to 400 degrees. Spray a 2-quart baking dish with non-stick cooking spray.
In a large non-stick skillet, combine olive oil and butter. Cook over medium heat until butter melts. Add onion and garlic. Cook until onion begins to be translucent, 4 to 5 minutes.
Raise heat to medium-high. Working in batches, add spinach to pan. Cook, stirring often, until spinach wilts, 3 to 4 minutes per batch. Repeat process with remaining spinach until all spinach is wilted, stirring often. To reduce liquid, cook for an additional 3 to 4 minutes, 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 and remove from heat.
Add 1 1/2 cups of shredded mozzarella, 1 cup of Parmesan and 1/2 cup Asiago, stirring well. Spoon into prepared dish.
Cover and bake in preheated 400 degree oven for 15 minutes. Remove cover and spread remaining 1/2 cup mozzarella over top. Bake until cheese is golden brown, about 10 minutes.