Heat the olive oil in a large stockpot over medium-high heat. Pack the spinach into the stockpot and cook, turning the spinach with tongs, until wilted, 2 to 3 minutes. Transfer the spinach to a colander set in the sink and let stand until cool. Using your hands, squeeze as much moisture out of the spinach as possible.
Put the artichokes and drained spinach in a food processor and pulse until coarsely chopped. Add the heavy cream and puree until smooth.
Pour the mixture into a large nonstick pan over medium-low heat. Stir in the Pecorino Romano, mozzarella and mayonnaise. Season with salt and pepper and cook until the mixture is hot and the cheese is melted, about 10 minutes.
Serve the dip warm with vegetables, crackers, crostini or chips for dipping.
Recipe courtesy of Rob Del Balzo, Nuttin' To It Restaurant