In a bowl, mix cream of chicken soup, cream of mushroom soup, and sour cream. Spread over the chicken.
Crumble the Ritz Crackers and spread on top of chicken. Dot top of casserole with butter pieces.
Bake the casserole until the crackers are browned, about 25 minutes.
Notes
To make ahead. Assemble the casserole without baking. Cover tightly with foil or plastic wrap and refrigerate. Remove from the refrigerator while the oven in preheating. Bake as directed.To store leftovers. Cool completely and store in an airtight container in the refrigerator for 3 to 4 days.To freeze. Cool completely, wrap tightly with plastic wrap, or store in an airtight, freezer-safe container. Freeze for up to 3 months. Thaw in the refrigerator overnight, reheat, and serve.