Delicious Twice Baked Spinach Potatoes

3 large baking potatoes½ c. milk½ c. soft cream cheese2 c. shredded sharp cheddar cheese, divided¼ c. finely chopped onionSalt, black pepper1 (10-oz.) pkg. frozen chopped spinach, thawed, drained and squeezed drySliced green onions, garnish 1. Preheat oven 400.2. Scrub…