In a large skillet, saute onion in oil until tender. Add garlic; cook 1 minute longer. Stir in the spinach, salt and pepper. Remove from the heat., In another skillet, cook pancetta over medium heat until crisp. Remove to paper towels with a slotted spoon; drain., In a greased 13x9-in. baking dish, layer the hash browns, spinach mixture and pancetta. In a large bowl, whisk the eggs, milk, 1/2 cup fontina cheese, 1/2 cup cheddar cheese, parsley, Worcestershire sauce, mustard and nutmeg; pour over casserole. Sprinkle with remaining cheeses., Bake, uncovered, at 350° for 30-35 minutes or until a knife inserted in the center comes out clean. Let stand for 10 minutes before cutting. If desired, sprinkle with freshly ground pepper and garnish with additional parsley.