In a large skillet over medium heat, saute the onions in the butter until soft. Stir in the garlic and saute for an additional minute.
3 tbsp butter, 1/2 onion, 2 cloves garlic
Stir in the flour until it's combined with the veggies. Cook, stirring, and another minute.
3 tbsp flour
Add the chicken broth and milk, a little at a time, stirring each addition until it's completely incorporated and smooth- no lumps! Continue until all the liquid's been incorporated. Continue cooking over medium heat until the mixtures reduced slightly and thickened.
1 1/2 cups chicken broth, 1/2 cup milk
Stir in the chicken, and season with salt & pepper, to taste. Stir in the sour cream and poppy seeds, until evenly incorporated. Season with salt & pepper, to taste.
2 chicken breasts, 8 oz sour cream, 1 tbsp poppy seeds, salt & pepper
Transfer the mixture to a 9x13 baking dish and use a spatula to spread it out evenly.
Melt the butter, and toss it with the crushed crackers coating them well. Sprinkle the cracker crumbs evenly out over top of the casserole.
2 tbsp butter, 1 1/2 cups crushed Ritz crackers
Baked for 30 minutes at 350 degrees, or until the crackers are golden brown and the casserole's hot & bubbly.
Serve over cooked white rice and enjoy!