Cook the noodles according to the package directions.
Brown the ground beef along with the onion. Drain the fat off the meat.
In a large bowl, combine the noodles, beef, peas, soups and sour cream. Pour the mixture into a greased 9x13 (or even a bit larger) greased baking dish.
In a small bowl, toss the breadcrumbs with the melted butter. Sprinkle the breadcrumbs on top of the casserole. The pan will be very full.
Cover the casserole with foil and bake the casserole in a 350 degree oven for 25 minutes, then uncover and bake an additional 15-20 minutes, or until is heated through and lightly browned on top.
Serve immediately.
Video
Notes
For the bread crumbs, we used leftover hamburger and hot dog buns that we had in the freezer. This is a great way to use up some of those spare pieces of bread.