Preheat your oven to 350°F (175°C) and lightly grease a 9x13 inch baking dish.
In a large mixing bowl, combine the cream of chicken soup, mayonnaise, and sour cream, stirring until silky smooth.
Fold in the diced celery, chopped onion, slivered almonds, and fresh lemon juice.
Add the cooked chicken to the mixture, folding gently to maintain texture. Then incorporate 1½ cups of the shredded cheddar cheese, reserving ½ cup for the top.
Season with salt and pepper, tasting and adjusting as needed.
Crush the Ritz crackers in their sleeve or place them in a ziplock bag and use a rolling pin for a controlled crush. In a separate bowl, combine the cracker crumbs with melted butter, stirring until every crumb is coated.
Transfer the chicken mixture to your prepared baking dish, spreading it evenly with a spatula.
Sprinkle the reserved ½ cup of cheddar cheese over the top, then distribute the buttery cracker mixture evenly across the surface.
Bake uncovered for 30-35 minutes, until the edges are bubbling and the topping turns a gorgeous golden brown.
Let sit for 5-10 minutes before serving to allow the casserole to set properly.