I fixed this yesterday to take to a birthday dinner for my friend Connie. I thought that it was delicious, and I always like something you can do in advance. The amounts are approximate. You'll have to taste and correct because I was just wingin' it.
Preheat oven to 350
1-2 tbl olive oil
1 tbl butter
1 small onion, chopped fine
1 fat garlic clove, chopped fine
2 pcks frozen, chopped spinach
Salt & pepper to taste
2 tbl butter
4 tbl flour
2 cups milk
1 cup grated Parmigiano Reggiano
1/2 cup grated sharp cheddar cheese
1/4 tsp cayenne pepper
1 1/2 tsp dry mustard
1 tbl Worstershire sauce
Salt and pepper to taste
Saute onion and garlic in olive oil and butter with a pinch of salt. Add spinach and cook til defrosted over medium heat. Raise heat. Push spinach to one side, tilt the skillet, and press on spinach to remove and evaporate excess liquid. Season with salt and pepper to taste. Remove spinach to a mixing bowl.
Make white sauce in same skillet. Melt butter over low heat. Add flour and cook, stirring, about 3 minutes, without letting the mixture brown. Add milk, stirring constantly. Raise heat and continue stirring until sauce boils. Lower heat and let simmer 3 minutes. Turn off heat and add cheeses and spices. Add sauce to spinach, stir, taste, and correct seasonings.
Place in buttered casserole dish and top with additional sharp cheddar. Cover and bake for 30 minutes until hot and bubbly. To do ahead, cover and refrigerate. Then place in the microwave for 5 minutes at 70% power, then into the oven for 30.