Preheat your oven to 350 degrees Lightly grease a 9-inch pie plate. You can also use a square 8-inch baking dish or any other baking dish with similar capacity.
Drain the artichoke hearts well. Place in a clean kitchen towel and squeeze to get rid of as much liquid as you can (You will need to rinse the kitchen towel after you're done). Chop them coarsely and set aside.
Thaw the spinach in the microwave. I place it in a microwave-safe bowl, cover, and microwave for 4 minutes. Place the thawed spinach in a colander and press on it with the back of a large spoon to get rid of as much water as possible.
In a large bowl, combine the sour cream, mayonnaise, garlic, red pepper flakes, Parmesan, and 3 oz cheddar. Mix in the chopped artichokes and the spinach.
Transfer the mixture to the prepared baking dish. Smooth the top out with a spatula. Sprinkle with the remaining cheddar.
Bake until golden and bubbly, about 20 minutes. Serve with fresh-cut veggies, with almond flour crackers, or with pork rinds.
Keep leftovers in the fridge, in an airtight container, for 3-4 days. You can also freeze the leftovers, then thaw them overnight in the fridge.