In a large skillet, heat the shortening over medium-high heat. Add the beef cubes and season with salt and pepper. Cook, stirring occasionally, until lightly browned, about 5 minutes.
Add the onion and celery to the pan and cook for an additional 3 minutes. Stir in the soy sauce and molasses and reduce heat to low.
Stir in the mushrooms, water chestnuts, bean sprouts, and reserved mushroom liquid. Simmer over low heat until the meat is cooked through and tender, about 10 minutes.
Serve the beef chop suey over cooked white rice and sprinkle with chow mein noodles. Drizzle with a bit of extra soy sauce to taste, if desired.