01 -
Turn the oven on to 375°F. Cook the pasta shells until they’re just tender, following the package guide.
02 -
Warm up the olive oil in a big pan. Toss in the diced onion, cooking for about 3-4 minutes until softened. Stir in garlic and let it cook for another minute.
03 -
Throw the spinach into the pan. Stir it around until it wilts, which takes roughly 2 minutes.
04 -
Dump the spinach, cheeses, egg, salt, and pepper into a big bowl and mix them together well.
05 -
Pour half the marinara sauce evenly into the base of an 8x8-inch or 9x9-inch baking dish.
06 -
Scoop the cheese-spinach mixture into each pasta shell and place them in the saucy baking dish.
07 -
Spread the rest of the marinara over the pasta shells and bake it for 20-30 minutes, letting it warm through.
08 -
Top with extra Parmesan cheese and basil if you want, then eat it right away.