Add the cut potatoes, carrots, and mushrooms to the slow cooker.
Add the all-purpose flour, table salt, and black pepper to a shallow bowl. Whisk to combine,
Add the beef cubes to the flour mixture and toss to coat the cubes.
Add the olive oil to a large skillet over medium high heat.
Add the meat to the pan and sear it on all sides (about 3-4 minutes).
Add the red wine to deglaze the pan. Scrape the bottom of the pan to get all the tasty brown bits to release from the pan.
Pour the beef and any liquid from the pan into the slow cooker.
Add the butter to the same pan. When the pan is hot, add the chopped onions. Sauté for 2 minutes, then add the mixture to the slow cooker.
Add the beef broth, tomato paste, fresh thyme, and Worcestershire sauce to the slow cooker and mix gently.
Set the slow cooker to the low setting and cook for 7 to 8 hours, until the beef and potatoes are fork tender.
With 15 minutes remaining, add the frozen peas to the mixture. Cover with the lid on and cook for an additional 15 minutes.
If the sauce is thin, add two tablespoons of butter to a saute pan and when the butter is melted, mix in two tablespoons of flour. Stir to combine and cook over medium heat for 2 minutes. This is a roux that will thicken the gravy.Add the liquid from the slow cooker to the roux and whisk until well combined. Heat until the sauce is thickened, then add it back to the slow cooker and stir to combine.If the sauce is too thick, add water or beef broth to thin it out. Serve with mashed potatoes, noodles, or the grain of your choice and garnish with chopped parsley.