I believe I was in girlscouts when I learned how to make these. They have great flavor and hardiness to them. It is one of my husbands favorite meals. Oh he still likes his mashed potatoes with them so he can enjoy the wonderful mushroomy gravy that is made from them as they cook. I serve these with fresh green beans. I always make enough for my husband to have for lunch at work too. It is also a recipe to play with. I have used min. rice in the burger recipe with beef broth stired in (enough for rice). I have made it with left over souped up min. rice as a stuffing.. you can play with it which I like about the recipe.
mix hamburger together with egg. press hamburger into 4-6 inch diameter round and 1/4 inch thick. (I use a sheet of plastic wrap and do it by hand, it doesnt need to be perfect but the plastic wrap makes it easier to fold over and place into the pan.)
place a scoopful of stuffing on one side of the hamb. patty, and fold over to make half moon shape, press around hamb to seal in stuffing. place into 9x13 pan.
open can of condensed cream of mushroom soup, pour into a bowl and whisk until spreadable. then cover the stuffed hamburgers evenly and cover pan with aluminum foil.
place in a preheated 350* oven for one hour. And enjoy.