Cook pasta al dente according to pasta package directions. Make sure not to over cook the pasta. Otherwise it will not be easy to fill and will fall apart. Drain and rinse with water so that pasta does not stick together.
In large bowl, beat eggs lightly. Then add ricotta, mozzarella, spinach, butter, salt and pepper. Mix until well blended.
Fill the shell pasta with the cheese mixture. Set aside.
Put a thin layer of spaghetti sauce on the bottom of a 9x13 baking dish. The arrange filled shell pasta on top.
Pour remaining spaghetti sauce on top. Sprinkle with parmesan cheese.
Cover with foil and bake for 30 minutes.
NOTE: Consider foil lining your baking dish for easy clean up. When entertaining, assemble this dish but don't bake until just before serving. Can be made the night before.