For the filling, I squeezed the sausage out of its casing and browned it in a skillet. Then I removed the sausage and sweated some chopped onion and garlic in the sausage drippings. I let the onion, garlic, and sausage cool before I combined them with the thawed and drained spinach, about a cup of ricotta, and one egg (lightly beaten). I seasoned with S&P and added a little nutmeg and crushed red pepper.
I boiled the shells until al dente, then let them cool slightly before stuffing with the filling. I layered tomato sauce in the bottom of the pan, and put some on top of the shells before wrapping the whole dish tightly in foil. I baked them in a 350 oven for around 40 minutes.
Our casserole dish isn't that big, so I had to squeeze the shells in there and do some layering- hence the slightly sloppy appearance. I love stuffed shells with just spinach and cheese, but the sausage really put these shells over the top. We only used three links, so we got a lot of the richness and flavor of sausage without all of the fat.