01 -
Preheat your oven to 350°F (177°C). Set aside a 3-quart baking dish.
02 -
Bring a large pot of salted water to the boil. Add the pasta shells and follow the package directions for cooking. Drain and rinse the shells with cold water.
03 -
Heat a wide skillet over medium-high heat. Add the sausage and cook until browned, about 10 minutes. Use a wooden spoon to break the sausage into small pieces as it cooks.
04 -
Stir in the garlic, tomatoes, and thawed spinach. Cook until heated through and the liquid reduces by half, about 2 minutes.
05 -
Remove the pan from the heat, then stir in the ricotta cheese. Taste and adjust seasoning with salt and pepper.
06 -
Add about 1 cup of marinara sauce to the bottom of the baking dish. Fill each shell with the sausage filling and arrange them in the dish. Scatter mozzarella cheese over the top.
07 -
Bake in the preheated oven until the tips of the shells begin to brown and the cheese has melted, about 25 minutes.
08 -
Warm the remaining marinara sauce and serve alongside the stuffed shells.