Prepare the Vegetables - Add potatoes, carrots, celery, onion, and thyme to the slow cooker.
Prepare the Beef - Cut beef into 1 ½" pieces, trimming off any excess fat or connective tissue. Combine with salt and pepper in a medium-sized bowl.
Brown the Meat - Heat a large skillet over medium-high heat. Add the olive oil. Once hot, add the beef in a single layer. Saute until golden brown on one side, 2 minutes. Flip and cook the other side for 2 minutes. Transfer to the slow cooker.
Deglaze the Pan - Reduce heat to medium, add garlic and saute for 30 seconds. Add balsamic vinegar. Turn heat to medium-high, deglaze the pan using a whisk to scrape any browned bits, and incorporate into the liquid.Reduce the sauce, frequently stirring, until 2 to 3 tablespoons of liquid remain, about 3 to 5 minutes. Transfer the liquid to the slow cooker.
Cook the Stew - Add beef stock and soy sauce to the slow cooker. Cover and cook on the High setting for 4 hours or the Low setting for 8 hours.
Thicken the Stew - Whisk together cornstarch and water in a small bowl. Add the slurry mixture to the slow cooker, and stir to combine. Cook on High setting for 30 minutes to 1 hour until the sauce becomes slightly thickened.
To Serve - Taste and season with more salt and pepper as desired. Serve garnished with parsley.
Notes
Make it Whole-30: Substitute soy sauce with coconut aminos. Substitute cornstarch with 6 tablespoons arrowroot flour (starch/powder) Bob’s Red Mill is recommended, mixed with 6 tablespoons water to make a slurry.
Storing:Cool and store in an airtight container in the refrigerator for up to 1 week. Freeze in a resealable plastic bag for 3 months. Defrost before using.
Reheating:Cover and reheat in the microwave on high setting in 30-second increments, stirring in between, until hot. Heat on the stovetop or medium heat until hot. Add more beef stock if needed.