Try to find two 3-4 lb. chuck roasts, and cut the excess slab of fat off the top. Cut into LARGE bite-sized pieces because beef shrinks when it cooks. You want to end up with nice big chunks! :) In large metal roaster that you can use on the stove, lightly brown meat on all sides over medium-high heat in a little oil. You may have to do this in frying pan(s). *Pepper beef lightly to liberally with coarse ground pepper as you add it to the roaster or frying pan. (Should take about 10 minutes.) When beef is lightly browned on the outside, add broth, onion, soup mix, A-1, garlic, horseradish, mustard, butter and a nice amount of salt. Add salt a 1/2 teaspoon at a time so you don't over do it. Bring to a boil, cover with lid, turn down heat and simmer for 1 1/2 hours. Stir occasionally. Add mushrooms, recover, and simmer 15-20 minutes longer. Remove lid. Mix cornstarch and cold water, add, stirring. Simmer, stirring only occasionally, for another 5 minutes til thickened a bit. Fold in cooked, drained noodles. Serve with warm crusty bread and butter, and a side vegetable such as green beans, broccoli or salad. *You can add another 1/2 bag more cooked noodles if you want to stretch this out. I make it hearty, full of lots of meat, though; when it's being considered as a "main dish". If you stretch it out though, you may need to add a cup or so of beef bouillon. Just see what you end up with, add as needed.
*If you accidently add too much salt, just add a few more Tbl. butter.
**This can be held on low heat for up to at least another hour no problem. Stir/fold now and then. Or put in a heated crockpot on low to hold.