8x8x2 pan
Preheat oven to 350 degrees F. Put a few tablespoons of sauce on bottom of glass baking pan then layer noodles (breaking to fit 3 across), ricotta, sausage (if using), mozzarella, spinach, parmesan, and sauce leaving a little space around all sides (about ¼ inch). Repeat layering until you have used up all of your supplies – aim to end with cheese then sauce on top.
Slowly pour the boiling water around all 4 sides of the lasagna, then cover tightly with foil. Place on the middle rack in your oven with a sheet pan on the rack below to catch any drips. Bake for an hour then remove the foil and bake 10 more minutes. Remove from oven and let sit for 10 – 30 minutes before serving.