To a medium bowl, add the mushroom soup, beef broth, optional Dijon, Worcestershire sauce, and whisk to combine.
Pour the liquid over the contents in the slow cooker, stir to combine, cover the the lid, and cook on high for 4 to 5 hours OR on low for 7 to 8 hours, or until done. Tip - At any time the beef is slow cooking and you feel like it needs a bit more beef broth, it's fine to add a bit more, to taste.
In the last 15 minutes of slow cooking, cook the egg noodles in a pot of boiling water according to package directions; drain and set aside.* (See Notes about why I don't cook the noodles in the slow cooker and cook them separately.)
Optionally, if you want a creamier sauce, after the beef stroganoff has cooked and has cooled a bit meaning it's not boiling nor bubbling, slowly you can add 1/2-cup heavy cream at room temperature while whisking vigorously as you add it. Tip - Do NOT add cold cream to hot beef liquid because the dairy proteins can separate, or break, and you will end up with a horribly ugly looking sauce after hours and hours slow cooking. So make sure the cream is at room temp and the beef stroganoff has cooled a bit if you are adding cream.
Plate a bed of noodles, top with the beef and gravy mixture, and serve immediately. Extra beef stroganoff will keep airtight in the fridge for up to 5 days and in the freezer for up to 4 months. Tip - Because the noodles will continue to absorb moisture, including any of the beef gravy or sauce, it's very important to store the beef mixture and the noodles separately in the fridge or freezer.
Notes
*It is possible to cook your noodles in the slow cooker but not my first recommendation.If you do go this route, you’ll want to remove all the cooked beef first, then let the noodles simmer in the sauce that remains. However, the pitfall here is that the noodles will soak up a lot of the liquid, so you may have to add more liquid. Either more beef broth or water. And then, they are prone to overcooking in a hurry and thereby disintegrating.Therefore, a much more tried-and-true and safer method is to cook the noodles in a pot of boiling water on the stove in the last 15 minutes of slow cooking your beef, according to the package directions. Drain and get them ready for all that luscious beef and gravy they’re soon to be piled high with!