Melt the shortening in a large skillet. Season the brisket with salt and pepper and place in the skillet. Add the onion and cook until the brisket and onion are browned. Add the sauerkraut and cover with boiling water. Cook over low heat for 2 hours or until the brisket is tender. Roll out the dough on a floured surface and cut into squares. Place on brisket and cover. Cook for 25 minutes and serve immediately.