Bring a pot of salted water to a rolling boil and drop in the pasta shells. Add in a couple extra in case some of them tear. Boil according to box instructions.
While the pasta cooks, combine ricotta, ½ cup shredded mozzarella, grated parmesan, an egg yolk, Italian seasoning, and salt in a medium mixing bowl. Set aside.
Preheat your oven to 350 degrees F, then rinse the cooked pasta shells with cold water so they’re no longer too hot to touch.
Flip each shell inside out to create a cup shape, then place one inside each muffin tin cavity.
Divide the ricotta cheese filling among the pasta cups, then top each one with a tablespoon of marinara sauce and the remaining shredded mozzarella cheese.
Bake for 8-10 minutes or until the cheese is melted and the filling is warmed through!