Heat olive oil in a pot over medium-high heat. Add shallots and garlic. Cook for 3-4 minutes until shallots are translucent.
Stir in tomato paste and cook for 1 minute until fragrant.
Add white wine, increase heat to high, and let it simmer rapidly until mostly evaporated (about 2 minutes).
Pour in tomato passata, vegetable stock, and salt. Stir, then simmer uncovered on low heat for 20 minutes.
Squeeze fresh spinach firmly to remove as much excess water as possible.
In a bowl, combine the squeezed spinach with ricotta cheese, Parmesan cheese, egg, nutmeg, salt, and pepper. Mix well.
Spoon the ricotta-spinach filling generously into each cooked pasta shell.
Arrange the stuffed shells in a baking dish over a layer of the prepared tomato sauce. Top with remaining sauce. Bake at 200°C (400°F) for 20-25 minutes.