Melt the butter in a big pan over medium heat, then add the onions and a tsp of Kosher salt.
Stirring often, cook for 15 to 20 minutes or until they begin to become caramel in color.
Garlic is added, stirred, and cooked for one minute.
After taking them out of the pan, set the onions aside.
After adding the canola oil, increase the heat to medium-high degrees.
Use the remaining salt and pepper to season the brisket.
Allow to brown for three to five minutes on each side.
Place the fatty side of the brisket into the slow cooker and cover with the onion-garlic mixture.
Cover the brisket with beer and Worcestershire sauce, then reduce the heat to low and simmer for eight hours.
To serve, cut against the grain.