Put chicken in a pot and cover with broth. Bring to a boil, reduce heat, cover, and simmer 15 to 20 minutes or until chicken is done. Remove chicken, let cool slightly, and shred or chop. Reserve ½ cup chicken broth, and save the remaining broth for later use (be sure to refrigerate or freeze).
Make Soup
Heat pot used to poach chicken over medium heat and add butter. Whisk in flour and whisk for 2 minutes. Slowly whisk in ½ cup chicken broth, then milk. Continue to whisk until mixture starts to boil. Boil for 1 minute then reduce heat to low. Stir in salt, pepper, garlic powder, onion flakes, paprika, and cooked chicken. Remove from heat {you just made cream of chicken "soup"}.
Prepare Casserole:
Stir 1 cup Greek yogurt and poppy-seeds into chicken mixture. (You can add a couple of tablespoons extra yogurt if you want). Put mixture in a 2 quart casserole dish coated with cooking spray.
If you are making this meal ahead of time, cover and refrigerate up to 24 hours**. Otherwise, proceed with directions.
Preheat oven to 350°. Combine melted butter and Ritz cracker crumbs. Top poppy-seed chicken casserole with buttery Ritz cracker crumbs. Cover and bake for 25 minutes. Uncover and bake 5 more minutes until topping is crispy. Let sit for 5-10 minutes before serving. Enjoy!
Notes
*If you don't want to poach the chicken you can use about 3 cups already cooked chicken. You will only need ½ cup chicken broth instead of 4 cups.*If you are making this ahead of time, be sure not to add Ritz until right before baking. Also, take the casserole out of the refrigerator before preheating oven. You don't want to put a cold casserole dish into a hot oven -- it might cause the dish to break.*You can get the whole wheat version of Ritz, but it doesn't make much of an improvement. I prefer to get the regular kind