Heat a large cast iron skillet over med-high heat. Add your butter or bacon fat. Season your beef with salt and pepper on all sides. Sear your beef about 4-5 minutes on each side till a dark golden color develops, this is your flavor, we aren't trying to cook it through. Place your beef over into the slow cooker.
Next, add the tomato paste to the beef drippings in your hot cast iron pan. Stir and cook about 1 min. Season your veggies with salt and pepper , add to the pan and saute for 2-3 minutes.
Lastly, pour about a cup of your bone broth and the Worcestershire sauce into the pan to de-glaze. Be sure to scrap up any bits off the bottom of the pan. This is more flavor! Now dump this mixture over your beef in the slow cooker. cover with the rest of your broth.
Set it to low and cook 9 hours. Don't remove the lid, you lose an hour of heat when you do! When it's done it will be fork tender, shred the meat to your liking. Serve with biscuits or crusty bread.