Heat the butter is a large skillet over medium-high heat and brown both sides of your roast (3-5 minutes per side). Turn burner to medium and remove roast.
While the roast is browning butter, oil, or spray your slow cooker insert and make your cornstarch slurry. To make slurry mix cornstarch and COLD water. Mix well. Set aside but if you set it aside for too long, just mix it again before using it.
Scrape down the sides and get all the brown bits and butter together. Add to beef broth and stir until incorporated. Allow to come to a boil.
Add the cornstarch slurry and stir. Add a lid and proceed to your crockpot.
Place the roast in the bottom of the slow cooker. Or on top your vegetables if you decided to add them.
Sprinkle with 1/2 of each of the seasoning packets, flip the roast and repeat.
Check the skillet gravy. If it’s slightly thickened, then slowly pour it over roast. Cover and cook on low for 6 to 10 hours.
When ready to serve: Remove roast and stir gravy well. Shred roast if desired and serve with gravy.
See Notes for a much simpler method for making slow cooker 3 packet roast.