Carefully open the corned beef bag and discard the liquid that is in the bag. Remove the brisket and spice packet. Rub the spices into the fat side of the meat.

Place the brisket, a sliced onion and beef broth inside your plastic bag and if using a vacuum sealer, seal the bag. If you do not have a vacuum sealer, you can use a zip top bag that you seal almost all the way. Slowly add the bag to the water bath until just below the top is submerged. Then seal the rest of the bag to ensure most of the air is out.

Fully submerge meat in water bath set to 180º F. Put a lid on and let it cook for 10-12 hours.

Remove from the water bath and use paper towels to completely dry the meat.

Pour oil into a large skillet and heat to high heat. Once the oil is shimmering add the corned beef and sear for about 2 minutes per side until golden.

Remove from the pan and slice against the grain to serve.