Boil the potatoes till just fork tender but not cooked all the way through; about 10-12 minutes depending on the size of your potatoes. Strain and set aside to cool
While potatoes are boiling, combine the sour cream, grated onions, cheddar cheese, cream of chicken soup and half of the melted butter to a blender, and process till just combined.
When potatoes are cool enough to touch, push them through the ricer, food mill or food processor, into a large bowl.
Stir in the creamy cheese mixture to the potatoes, and gently mix in till just combined. Place in a casserole dish.
In a small bowl, combine the remaining melted butter with the bread crumbs, then sprinkle on top of the casserole.
Bake for 30 minutes, till heated through and crust is golden brown.
To make homemade Cream of Chicken Soup
Combine the chicken broth and ½ cup of milk to a sauce pan and heat till you achieve a gentle boil.
While broth and milk are warming, in a small bowl, whisk the flour and seasonings into the remaining 1 cup milk until a smooth, thick mixture forms.
Pour the flour and milk mixture into the saucepan with the broth mixture and stir over low heat till the mixture simmers. Continue to simmer and stir until the mixture is smooth and thick, about 5 minutes.
Notes
You can find potato ricers at most home goods stores, including Williams Sonoma, Bed Bath & Beyond, and of course Amazon.You can swap out crushed corn flakes for the bread crumb topping.