Cut the beef into one-inch cubes, trimming off large pieces of visible fat. Pat completely dry, then season with garlic salt and pepper. Lightly sprinkle flour over the meat and toss to coat evenly.

Heat 2 tablespoons of olive oil in a skillet over medium-high heat. Sear the meat in batches, about 45 seconds per side, until browned. Remove the beef and set aside.

In the same skillet, add 1 tablespoon of butter and white wine to deglaze the pan, scraping up any browned bits. Cook onions and mushrooms for 4 minutes, then add minced garlic for another minute before removing from heat.

In your slow cooker, whisk together beef broth, bouillon, red wine vinegar, Worcestershire sauce, and Dijon mustard. Add the browned beef along with the cooked mushrooms, onions, and garlic.

Cover and cook on high for 4-5 hours or on low for 8-9 hours. Check as it nears the end of cooking time.

In a bowl, mix cornstarch with 1/4 cup cold water. When cooking time is nearly done, whisk this mixture into the slow cooker and switch it to warm.

In a medium bowl, whisk the sour cream with 1 cup of liquid from the slow cooker until smooth, then stir it into the slow cooker.

For added creaminess, consider adding condensed cream of mushroom soup.

Turn off the heat and swirl in the remaining cold butter for a velvety finish.

Serve over wide egg noodles or toss them straight into the slow cooker and stir to combine before serving.