Cook pasta in boiling water according to package directions. Drain. Set aside.
In a medium bowl combine sour cream, pasta sauce and 1 1/2 cups mozzarella cheese. Mix well. Add pasta mixing to combine. Stir in pepperoni. Place in a greased 3 qt casserole dish. Sprinkle with remaining mozzarella cheese.
Cover and bake for 15 minutes. Uncover and continue to bake 10-15 more minutes or cheese has melted and it's heated through.