5 tablespoons butter, divided
1 medium onion, sliced thin
3 garlic cloves, minced
2 (10-ounce) packages baby portebello mushrooms, sliced
2 (6-ounce) packages prewashed baby spinach
3 tablespoons flour ( or a gluten free flour)
3 cups milk
2 cups Swiss cheese, shredded
1 teaspoon salt
1/2 teaspoon pepper
1/4 teaspoon nutmeg
2 teaspoons lemon juice
5 cups cooked brown rice
4 cups cooked, shredded chicken – roast boneless chicken breasts in 375 degree oven for 25 – 30 minutes
In a large saucepan, melt 2 tablespoons of the butter over medium high heat. Add the onions and cook for about 6 – 8 minutes. Add the garlic and mushrooms and cook for an additional 8 minutes or until softened. Add half of the spinach and cook, stirring constantly, until spinach begins to wilt. Add remaining spinach and cook to wilt. Remove from pan to a large bowl and set aside.
In the same saucepan over medium high heat, add the remaining 3 tablespoons of butter and melt. Whisk in the flour and cook for 1 minute. Slowly whisk in the milk and cook for about 5 minutes, whisking occasionally until mixture comes to a boil and thickens. Remove from heat and whisk in the cheese until melted. Add the salt, pepper, nutmeg and lemon juice. Pour cheese mixture over the spinach mushroom mixture and stir to combine. Stir in the rice and chicken. Transfer mixture to a greased 9 x 13 inch (4-quart) casserole dish.
***At this point, the dish can be cooled, covered and refrigerated overnight or frozen for up to a month. Either bake as directed below directly from the refrigerator or thaw the frozen casserole for 24 hours in the refrigerator before baking as directed.***
Bake, covered with foil in a preheated 375 degree oven for 35 – 45 minutes or until hot and bubbly.