Preheat the oven to 350°F.

In a mixing bowl, stir together the artichoke hearts, onion, mayonnaise, sour cream, and Parmigiano-Reggiano. Transfer the mixture to an 8-inch or 9-inch round deep-dish pie plate or square baking dish, spreading it evenly.

Bake the dip until it is bubbling and its surface is lightly browned, about 30 minutes. Place the baking dish on a trivet on the serving table and accompany with bowls of Fritos Scoops for dipping.