Bring a large pot of salted water to a boil, then add the pasta shells. Cook for 10-12 minutes until just al dente, then drain and set aside.
While the pasta cooks, heat olive oil in a skillet over medium heat. Add minced garlic and sauté until fragrant, about 30 seconds, filling the kitchen with a warm, garlicky aroma.
Add the drained spinach to the skillet and cook until wilted, about 2 minutes. Remove from heat and let cool slightly.
In a mixing bowl, combine ricotta, the sautéed spinach and garlic, grated Parmesan, and a pinch of salt and pepper. Mix until smooth and creamy, adjusting with a splash of milk if needed.
Use a small spoon or piping bag to carefully stuff each shell with the ricotta mixture, gently filling the hollow cavity and trying to keep the shells upright.
Spread a thin layer of tomato sauce at the bottom of your baking dish, then arrange the stuffed shells in a single layer, open side up.
Pour the remaining tomato sauce over the shells, then sprinkle shredded mozzarella evenly on top. Cover with foil to keep the moisture in.
Bake in a preheated oven at 180°C (350°F) for 20 minutes covered, then remove the foil and bake for an additional 10 minutes until bubbly and golden around the edges.
Let the dish rest for 5 minutes out of the oven, allowing the flavors to settle and the cheese to set slightly.
Garnish with extra Parmesan or chopped fresh herbs if desired, then serve warm, enjoying the imperfect, joyful chaos of this cozy family dish.
