01 -
Heat your oven to 375°F and cook the pasta shells just until tender using the directions from the package.
02 -
Take a large skillet, warm up the olive oil, and cook the onion for around 3-4 minutes. Then, toss in the garlic and let it cook for one more minute.
03 -
Add the spinach to the skillet and keep cooking it for about 2 minutes until it softens and wilts.
04 -
Take a large mixing bowl and mix together the spinach mixture, ricotta, mozzarella, Parmesan, egg, salt, and pepper.
05 -
Cover the bottom of an 8x8 or 9x9 baking dish with a layer of marinara sauce (about half of it).
06 -
Spoon the cheesy spinach filling into the shells and arrange them in the baking dish over the marinara layer.
07 -
Pour the rest of the sauce on top, then bake for 20-30 minutes until warm and bubbly.
08 -
Sprinkle with grated Parmesan and fresh basil if you like, then serve while hot.