In a small bowl mix the brown gravy mix, BBQ sauce and beef stock. Pour the mixture in the crockpot on top of the beef, gently mix.
Cook the cube steak for 4 hours on high or 8 hours on low.
With one hour of cooking left, whisk together cornstarch and water, forming a slurry that will thicken the sauce (add more water as needed). Add to the crockpot and stir.
When the beef is cooked add the half and half at the last minute.