Spray the inside of your slow cooker with nonstick spray for easy cleanup.
Layer the potatoes, carrots, and onion in the bottom of the crock. Sprinkle with a pinch of salt and pepper.
Pat the cube steaks dry with paper towels.
Mix the onion powder, garlic powder, thyme, smoked paprika, black pepper, and salt in a small bowl.
Season both sides of the cube steaks with the spice blend.
Whisk together beef broth, Worcestershire sauce, tomato paste, and Dijon until smooth.
Stir in the minced garlic.
Place the seasoned cube steaks on top of the vegetables.
Pour the gravy mixture evenly over everything.
Cover and cook on Low for 6–7 hours (best tenderness) or High for 3–4 hours, until the meat yields easily to a fork and the potatoes are soft.
Whisk cornstarch and cold water until smooth.
Stir the slurry into the crock. Add butter if using.
Cover and cook on High for 12–15 minutes until the gravy thickens and looks glossy.
Taste and adjust salt and pepper.
Garnish with chopped parsley.
Serve right from the crock over the potatoes and carrots, with extra gravy spooned on top.
