Preheat your oven to 350°F and position a rack in the center. While the oven heats, shred or dice your cooked chicken if you haven't already, and measure out all your seasonings into a small bowl. Crush about three-quarters of the Ritz crackers into varying sizes—some finely crushed, some into larger pieces—this creates a better texture than uniformly crushed crackers. Leave the remaining crackers whole for visual appeal on top.

In a large mixing bowl, combine the cream of chicken soup and sour cream, stirring until smooth and well combined. Add the seasoning mixture from Step 1 and stir to distribute the spices evenly throughout. Fold in the shredded chicken gently until all pieces are evenly coated with the creamy sauce. I like to taste a small spoonful and adjust seasonings here if needed—it's your last chance to fix the flavor before baking.

Transfer the chicken mixture to a 9x13 inch baking dish (or similar size casserole dish) and spread it into an even layer. The mixture should fill about two-thirds of the dish, leaving room for the topping. Smooth the surface gently with a spatula but don't compress the mixture too much—you want it to stay light and creamy when baked.

Toss the crushed crackers from Step 1 with the melted and cooled butter until all pieces are evenly coated. Scatter this mixture evenly over the chicken base, pressing down gently so it adheres but doesn't sink into the cream. Arrange any whole crackers you reserved on top for a rustic presentation. Bake for 20-30 minutes until the cracker topping is golden brown and crispy, and the sauce bubbles slightly around the edges.

Remove the casserole from the oven and let it rest for 5 minutes before serving. I find this allows the sauce to set slightly, making portions hold together better when you scoop them out. The casserole will still be hot and the crackers will stay crispy on top.