Cook pasta according to package directions until al dente.

Drain pasta and run cold water over the shells to stop them from overcooking.

Meanwhile, in a medium bowl, combine ricotta, pesto, cheese, egg, and spinach and mix well.

Preheat oven to 350ºF.

Spread 1 cup of pasta sauce in the bottom of a 9×13 inch baking dish.

Stuff the shells with 2-3 Tbsp. of ricotta mixture and place in the baking dish.

Once all the shells are stuffed and the baking dish is full, pour the remaining 2 cups of pasta sauce over the shells and spread evenly.

Bake for about 30 minutes or until pasta sauce bubbles up around the edges.