Preheat oven to 400°F. Heat olive oil in large sauté pan over medium heat, add spinach and cook 1-2 minutes to wilt. Remove to plate to cool. Squeeze excess water from spinach. Set aside.
In small bowl, combine half of spinach and half of chopped artichoke hearts. Stir in softened cream cheese and ½ cup parmesan. Stir in shallots and 1 tablespoon garlic. Pour mixture into oven-safe baking dish and bake for 15 minutes or until mixture is toasted on top and heated through. Remove from oven; cover to keep warm and set aside.
Meanwhile, cook pasta according to package directions; drain and set aside. In medium pot, melt butter and whisk in flour. Continue whisking vigorously over medium high heat until roux becomes golden brown. Add milk slowly, 1/2 cup at a time, whisking during each addition. Bring mixture to boil. Add mustard, pepper, 1 tablespoon garlic, remaining cheeses and sriracha sauce. Stir in reserved spinach and artichokes, mixing until evenly incorporated.
Pour pasta into cheese mixture; mix to ensure all pasta is coated evenly. Plate and top with generous spoonful of warm spinach and artichoke mixture. Serve.
1 9-ounce package frozen spinach may be substituted for fresh. Thaw and drain spinach, squeezing to remove excess liquid.