Spray the inside of your slow cooker with nonstick spray for easy cleanup.
Add the diced onion, spinach (make sure it’s wrung dry!), chopped artichoke hearts, cream cheese, sour cream, mayo, milk, shredded mozzarella, parmesan, garlic, salt, pepper and nutmeg (if using) directly to the slow cooker.
Cover and cook on LOW for 1 hour. Stir everything together well.
Cover and continue cooking on LOW for another 1 hour, until everything is melted, creamy, and piping hot.
Give it a final stir. Taste and add extra salt, pepper, or red pepper flakes if desired.
Serve warm (or even chilled!) with your favorite dippers like tortilla chips, pita bread, crackers, or sliced veggies.
