Sauté onion and garlic in butter and/or olive oil over medium low heat. Add a dash or two of crushed red pepper flakes. In large bowl, combine onions, artichokes, spinach, mayo, sour cream, cream cheese, and parmesan cheese. Season with salt, pepper, paprika, cayenne pepper, and hot sauce to taste. Stir everything together until all the ingredients are incorporated. If necessary, add more mayo and sour cream until mixture is smooth, creamy, and spreadable. Place in cast-iron skillet or small dutch oven. Top with extra parmesan and the pepper jack cheese. Bake for 30-40 minutes until hot and bubbly. Remove from oven and serve immediately with tortilla chips, bagel chips, pita, or crudité.