This was one of the comfort foods from my childhood. Mom was adept at stretching a small amount of meat into a meal for eight people.
Yet she loved to "dress up" the food she served, even just for her family. If fresh mushrooms were available, they were sliced and added with the onions. Canned mushrooms were added with the soup. No mushrooms? No problem.
As kids, we probably seldom noticed anyway, but only truly appreciate her resourcefulness now. But isn't that the way it always goes? I miss you every day, Mom. xoxox =^..^=
In a skillet, heat enough oil to coat the bottom. Add the onions and saute until tender. If you have fresh mushrooms, add them with the onions.
Meanwhile, stir up some flour, salt, and pepper in a shallow dish. Dredge the steak pieces through the flour mixture...
...and add to the onion in the skillet. Stir often.
Start heating a pot of water to boiling for the noodles around now.
When the meat is cooked, add the can of cream of mushroom soup and milk to the skillet. (Mom always put the milk into the empty soup can & stirred it around to get all of the soup out, but she WAS a child of the Great Depression!) Stir well. Drain & add the canned mushrooms, if you're using them.
NOTE: If the sauce is too thick, add water, but read the next step to determine how much.
At this point, decisions must be made. If you have a tender cut of steak, this sauce is done when it is heated through. In this case, don't add too much water to the sauce! However, if you're like me and working with a food budget, you might have picked a less expensive cut of meat (or even beef cubes). In that case, thin out the sauce with water, turn the heat to SIMMER, cover the skillet, and stir every 10 minutes for an hour or so. (I like to cook it for about 90 minutes, unless I'm in a rush. My test for doneness is when the steak can be cut with a fork.) If the sauce is still thin when the meat is done, remove the lid and increase the heat, stirring more often.
When the water in the pot is boiling & the sauce is close to being done, add the noodles and stir well. Cook to desired firmness. (In my family, al dente is still "raw.") Drain & set aside until the sauce is done. It's OK if it cools because it will heat up immediately when you add it to the sauce!
When the sauce is done, you can stir in the sour cream, if desired. Add the noodles and mix well.