Chop garlic and onion, sauté together with just a tiny bit of butter until translucent. Cut steak into bite-size strips, discarding as much fat as you can, add to garlic and onion. Add beef stock, stir, and simmer uncovered for 20 minutes. Sauté mushrooms in a little butter in a separate pan, then add to the Stroganoff. Boil noodles until just done, drain. When everything is ready, stir the sour cream into the Stroganoff. Serve over noodles.