Heat olive oil in a large skillet over med-high.  Add onion and cook, stirring occasionally, until soft, about 4 minutes. Add the garlic and cook, stirring, 30 seconds.

Add the sausage and cook, breaking it up with a wooden spoon, until browned, about 5 minutes.

Add the spinach, 1/2 tsp salt, and pepper to taste and stir until heated through, about 2 more minutes.  Remove from the heat and let cool completely.

Combine the spinach mixture, ricotta, 1 cup mozzarella, the Parmesan, parsley and 1 tsp salt in bowl.  Stuff each shell with about 2 T of the filling and set aside.

Preheat oven to 350.

Melt the butter with the garlic in a medium saucepan over medium heat. When the butter begins to foam, add the flour and whisk constantly until lightly golden, about 1 minute. Add the milk and cream, bring to a simmer and cook, whisking constantly, until the sauce is thick enough to coat a spoon, 2-3 min. Remove from the heat and whisk in the Parmesan, 1/4 tsp salt, and nutmeg to taste.

Brush a 9 x 13 ” baking dish with olive oil and pour in about 2/3 of the cheese sauce.  Add the stuffed shells and top with the remaining cheese sauce.  Cover with foil and bake 20 minutes.

Uncover and top with the marinara sauce and the remaining 1 cup mozzarella: continue baking until the sauce is bubbly, 15-20 minutes.  Serves 8