Method
- Set an oven rack in the middle position and preheat the oven to 400 F. Lightly grease a 9-inch round or square baking dish with a small dab of butter or a spray of cooking oil so the dip does not stick.
- Place the thawed spinach in a clean kitchen towel or several layers of paper towel. Twist and squeeze hard over the sink until no more water drips out; this step matters because wet spinach will turn your dip watery and thin instead of creamy.
- Put the squeezed spinach in a large mixing bowl and use your fingers to break up any clumps so it will mix in evenly.
- Add the chopped artichoke hearts to the same bowl. Blot them with a paper towel first if they seem very wet.
- Add the softened cream cheese, sour cream, and mayonnaise. If your cream cheese is still hard, microwave it on a plate for 15 seconds to soften; it should give easily when pressed with a spoon.
- Add 3/4 cup of the mozzarella (save the rest for topping), 1/4 cup of the Parmesan (save the rest for topping), the minced garlic, salt, pepper, and red pepper flakes if using.
- Stir everything together with a rubber spatula until fully combined and no white streaks of cream cheese remain, about 1 to 2 minutes of mixing.
- Scrape the mixture into the prepared baking dish and spread it into an even layer with the back of the spatula, pushing it into the corners.
- Sprinkle the remaining 1/4 cup mozzarella and 1/4 cup Parmesan evenly over the top.
- Bake uncovered for 22 to 25 minutes, until the edges are bubbling vigorously and the cheese on top is melted with light golden brown spots. If after 25 minutes the top has not browned, switch the oven to broil for 1 to 2 minutes, watching constantly through the oven door so it does not burn.
- Carefully remove the dish from the oven using thick oven mitts; the dish and its handles will be extremely hot. Set it on a trivet or folded towel, not directly on your countertop.
- Let the dip rest for 5 minutes before serving; it will be lava-hot straight out of the oven and needs this time to firm up slightly so it scoops instead of running everywhere.
- Serve warm with sliced French bread or tortilla chips for dipping. Leftovers keep in an airtight container in the refrigerator for up to 3 days and reheat well in a 350 F oven for about 10 minutes.
Tips
Squeezing the spinach completely dry is the single most important step; skipping it is the number one reason this dip turns out soupy.
Softening the cream cheese before mixing prevents lumps, so set it out on the counter at least 30 minutes ahead or use the quick microwave trick in step 5.