In a large pan, fry italian sausage, beef and onion together until browned. Drain any extra fat.
Stir in spinach and garlic and cook 1-2 minutes. Remove from the pan (set aside) and wipe clean with a paper towel.
While your meat is cooking, cook your noodles according to the package. Drain and set aside to let cool so you can handle them. I often soak mine in some cold water for a few minutes.
In the frying pan melt the butter. Whisk in the flour until smooth and cook 1 minute.
Stir in milk, 1 cup at a time, whisking and cooking until thickened after each addition. When all milk has been added and mixture is thick, stir in sausage mixture, tomato sauce, salt, chipotle peppers (less for less heat, more for more heat) and tomatoes. Adjust seasonings to taste.
Assembly:Spray two 9x13" pans with non stick spray (I use one foil pan for the freezer lasagna, and keep one to bake the next day). Line each pan with 3 noodles. Top the noodles in each pan with ⅙ of the sauce (you're just trying to keep the sauce spread evenly throughout the dish). Top with a sprinkle of cheese. Repeat layers two more times: 3 noodles, ⅙ of the sauce, sprinkle of cheese. 3 noodles, remaining sauce, remaining cheese.
To bake:Set in the fridge until ready to bake or place right into an oven preheated to 350 degrees F. Bake for 45 minutes - 1 hour until heated through and cheese starts to brown. If your cheese begins to look too dry, cover with a piece of tin foil sprayed with non stick spray. Let sit 5 minutes before slicing.
!To freeze: Spray a piece of plastic wrap with non stick spray and place spray-side down on top of the lasagna (you don't want that cheese to stick while it's freezing!). Cover with a piece of tin foil and write the date and name of the dish. I also write a reminder to take the plastic wrap out before baking. Freeze flat. On the day you want to eat it, remove from the freezer in the morning and let thaw. It won't be completely thawed by the time you go to bake, which is fine. You can also pop right into the oven from the freezer, provided you used a foil baking pan, you'll just want to make sure the middle is hot before serving. Bake at 350 degrees for at least 1 hour, up to 1.5 hours, until heated through.