Stir together chopped artichoke hearts, cream cheese, mayonnaise, sour cream, garlic, mozzarella cheese, gruyere cheese, Parmesan cheese and crushed red pepper flakes in a large mixing bowl until combined.
Transfer to a 1 ½ quart baking dish and spread evenly.
Bake (uncovered) for 30 to 35 minutes or until heated through and bubbling around edges.
Allow to rest 5 minutes before serving. Serve sprinkled with sliced green onions.
Notes
Storage: Once cooled, store in an airtight container in the fridge for up to 3 to 4 days.
Make-Ahead: Cover baking dish and refrigerate overnight. Remove from fridge about 30 minutes before baking. Bake as directed (uncovered).