Preheat your oven to 375 degrees F (190 degrees C).
Rinse the spinach thoroughly and remove any tough stems. Roughly chop and set aside.
In a large skillet, heat the olive oil over medium heat. Add the onion and garlic and sauté until the onion is translucent and the garlic is fragrant.
Add the chopped artichoke hearts to the skillet and continue to sauté for 2-3 minutes. Then add the spinach in batches, allowing each batch to wilt before adding the next.
Once all the spinach is wilted, remove the skillet from the heat and set aside
In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise until smooth. Stir in the Parmesan and Gruyère cheeses. Add the crushed red pepper flakes, salt, and pepper, and mix until well combined.
Add it to the cheese mixture to the spinach and stir until well combined.
Transfer the mixture to a baking dish and sprinkle the top with the mozzarella cheese.
Bake in the preheated oven for 20-25 minutes, or until the top is golden and bubbly.
Notes
Cheese Variations: While Parmesan and Gruyère are recommended, feel free to play around with other types of cheese. Monterey Jack or white cheddar could be great alternatives for a different flavor profile.
Go Dairy-Free: If you're dairy-intolerant or vegan, you can swap the cream cheese, sour cream, and mayo for dairy-free alternatives. There are some fantastic vegan cheeses out there too!
Add Protein: Want to make your dip a bit heartier? Consider adding some cooked, shredded chicken or cooked, crumbled bacon.
Heat Things Up: If you're a fan of spicy foods, feel free to add more crushed red pepper flakes or even some diced jalapeños for an extra kick.
Fresh vs. Frozen Spinach: This recipe calls for fresh spinach, but if you're in a pinch, frozen spinach can work too. Just make sure to thoroughly thaw and drain it to avoid adding extra moisture to your dip.
Serving Style: This dip is fantastic served hot from the oven, but if you're hosting a party, consider keeping it warm in a small slow cooker or fondue pot so it stays melty and delicious throughout the event.