Mashed Potato Tart Recipe

pastry for 1-crust, 9-inch deep pie
1 pkg.(10 oz.) frozen chopped spinach
2 cups mashed potatoes, made from instant flakes according to package instructions
1 medium-size onion, chopped
1/4 lb. mushrooms, sliced
2 oz (4 tablespoons) butter
1 garlic clove, chopped
10 tablespoons grated Parmesan cheese
1/2 cup heavy cream
1 egg
1 tsp. salt
freshly ground pepper

Line a deep pie plate(6-cup capacity) with the pastry, allowing a 1-inch overhang. Cook spinach and drain very well. Mix spinach and mashed potatoes. Saute onion and mushrooms in butter for 5 minutes.Add garlic and saute for 1 to 2 minutes more. Scrape into potato-spinach mixture. Add 8 tablespoons of the cheese, the cream, egg, salt, and pepper to taste. Turn into prepared pastry shell. Fold up the 1-inch overhang over filling, leaving the center of pie exposed. Sprinkle with remaining 2 tablespoons cheese. Place in a preheated 375 degree F. oven and bake for 4 to 5 minutes.