Drain and place in 9 X 13 baking dish, or something of similar size.
Layer 1 cup of cheese over tortellini.
Season chicken with salt and pepper and saute in olive oil on low to medium heat until no longer pink. Remove from pan and layer over cheese and tortellini.
Saute onion in same pan until onion is translucent. Add chicken broth.
Mix in flour. Add remaining 1 cup of cheese, stir until melted, whisking out any lumps.
Add sour cream and stir until well blended. Pour over chicken and tortellini mixture. Cover and bake for 45 minutes. Serve and enjoy!
Notes
This recipe can be made ahead. If baking from refrigerator, bake 15 minutes longer.