Par-cook the pasta shells, according to package instructions. Drain the shells and cool them on a platter.
Preheat the oven to 400°F (200°C).
In a large skillet, cook the sausage, breaking them into small pieces. Transfer the browned sausage onto a plate lined with paper towel to drain the excess grease.
Wipe off excess grease from the skillet and pour the pasta sauce. Add the sausage and bring it to simmer over medium low heat until heated through.
Pour the meat sauce into a 9×13-inch (23x33cm) baking dish.
In a medium bowl, mix together ricotta cheese, parmesan cheese, eggs and pesto. Transfer the ricotta mixture into a pastry bag with round tip, or a ziplock bag with one corner cut.
Fill the pasta shells with ricotta mixture and arrange them in the baking dish with the meat sauce.
Top the pasta with grated mozzarella cheese. Cover with aluminum foil and bake for 30 minutes, or until bubbling.
Remove the foil and bake for another 10 minutes.
Rest the dish on wire rack for 10 minutes. Garnish with grated parmesan and fresh basil, if desired, and serve!