Preheat oven to 350°F. In a cast iron pan or medium skillet (preferably one that is both stovetop and oven-safe), saute the spinach and garlic in 2 tablespoons of butter until the spinach is wilted and the garlic fragrant.
Mix together cream cheese, 1 cup of jack cheese, 1/2 cup parmesan cheese, sour cream, and artichoke hearts. Combine with the spinach mixture.
Spread ingredients in a single layer in the skillet or a baking dish. Bake for 20 minutes. Remove from oven to cover with remaining 1 cup of jack cheese and 1/2 cup of parmesan.
Bake until brown and bubbly or broil for just a couple minutes longer to melt and brown the cheese.
Serve hot with tortilla chips, baguette slices, or thick crackers.