Heat a large skillet over medium heat. Cook beef in hot skillet, stirring occasionally, until some of the fat from the meat renders, 1 to 2 minutes; add onion and saute the mixture until the beef is completely browned, about 5 minutes more.
Pour water into the skillet; add beef bouillon. Reduce heat to low and cook mixture at a simmer until the liquid is mostly evaporated, about 90 minutes.
Stir cream of mushroom soup into the beef mixture; continue cooking until heated through, 5 to 7 minutes.
Bring a large pot of lightly salted water to a boil. Cook egg noodles in the boiling water, stirring occasionally until cooked through but firm to the bite, about 5 minutes; drain. Divide noodles between 4 plates and spoon beef mixture over the noodles.