Step 1

Cook pasta according to package directions; drain and rinse under cold water until completely cool. Drain thoroughly.

Step 2

Preheat oven to 350° F. Squeeze as much water as possible from the thawed spinach.

Step 3

In a large bowl, stir together the spinach, mozzarella, ricotta, carrots, egg whites, pepper and nutmeg until thoroughly blended.

Step 4

Line the bottom of an 11 x 7-inch baking dish with 1/2 cup tomato sauce. Divide the ricotta mixture among the pasta shells, pressing the filling into the shells with spoon to completely fill each shell.

Step 5

Arrange the shells side by side in a baking dish. Coat the shells with an even layer of the remaining tomato sauce. Sprinkle with Parmesan cheese, if desired.

Step 6

Bake until the center of the shells are heated through and the sauce is bubbling (about 40 minutes). Let stand 10 minutes before serving.