This heavy dish is great for dinner OR brunch, warm OR cold (family recipe).1 pound sweet Italian sausage links, casing removed6 large eggs20 ounces frozen chopped spinach, thawed, squeeze dry or 1 pound fresh salad spinach leaves, stemmed1 pound mozzarella cheese, shredded5 1/2 ounces (1/2 container) ricotta cheese1/8 teaspoon pepper10 to 11 ounces piecrust mix or 2 (9-inch) deep dish pie crustsPreheat oven to 375 degrees F. Crumble sausage in a medium skillet and brown meat over medium heat, breaking up with a spoon. Drain on paper towels.If using fresh spinach, bring a large pot of water to a boil and put spinach in water. Boil 1 minute and drain; squeeze dry.Separate 1 egg. Combine 5 eggs with 1 egg white, sausage, spinach mozzarella, ricotta and pepper and set aside.Prepare pie crust mix if using. Lay 1 pie crust in pie pan and spoon mixture into it. Lay another crust on top and flute with a stand-up edge. Carefully cut a 2-inch circle out of the top crust.Mix egg yolk with 1 tablespoon water and brush on top of pie. (Can decorate with scraps of dough.) Bake for 1 hour, 10 minutes until golden and bubbly. Check crust after 1 hour and put foil on edges to prevent over-browning. Let stand 10 minutes and cut OR chill uncovered until cold; cover and refrigerate until serving cold.