Bring a large pot of generously salted water to a boil. Add shells and cook until almost al dente.
Drain pasta, then place shells on a large baking sheet (so they won't stick together). Set aside.
Prepare Filling:
While pasta is cooking, heat olive oil in a large skillet over medium heat. Add garlic and red pepper flakes to oil and cook until fragrant, about 30 seconds, stirring constantly.
Stir spinach into pan and cook until just wilted. Remove from heat and season to taste with salt and pepper.
Transfer spinach to a fine mesh strainer, then press out excess liquid with the back of a spoon.
Drain artichokes in a strainer, as well, pressing out excess liquid. Place artichokes on a few layers of paper towel, then cover with more paper towels, and press out more liquid.
Mix together ricotta, Parmesan, Italian blend cheese, egg, salt, and pepper. Then, stir in spinach and artichokes. Season with additional salt and pepper to taste, if desired.
Prepare White Sauce:
While pasta and spinach are cooking, heat milk in microwave until warm, about 1 to 2 minutes. Set aside.
Melt butter in a large skillet over medium heat, then stir in garlic and cook until fragrant (about 30 seconds), stirring constantly.
Sprinkle flour over butter and cook, stirring constantly, for about 2 minutes or until golden.
Whisking constantly, slowly add milk. Bring mixture to a boil, then reduce heat to a simmer.
Cook until thickened (about 10 minutes), stirring frequently. Sauce should coat the back of a spoon when ready. Remove from heat, then add a dash of nutmeg and season generously with salt and pepper to taste.
Assemble Stuffed Shells:
Preheat oven to 350 degrees. Spray a 9 x 13-inch baking pan (or larger) with nonstick spray, then coat the bottom with about ½ of the white sauce.
Fill shells with a generous spoonful of filling and place in baking pan. (Crowd shells together to fit pan, if necessary.)
Pour remaining sauce over filled shells, then sprinkle with Italian blend cheese.
Cover pan with foil and bake for 30 minutes or until hot. Remove foil and continue baking until stuffed shells lightly golden in spots, about 5 to 10 minutes more.
Serve shells hot, sprinkled with additional Parmesan cheese, if desired. Enjoy!
Notes
Short on time? Feel free to replace the homemade béchamel sauce with a jar of your favorite pasta sauce ... either marinara or Alfredo will work.