Pre-heat oven to 375 degrees. Pat the brisket dry and season generously with salt and pepper on each side. Sear the brisket in a large cast iron pan or Dutch oven on high heat, 6-7 minutes per side, until the brisket is golden brown, fragrant and the fat has mostly rendered out. Use tongs to remove from the pot and set aside.

Lower the heat to medium and without cleaning the pot, add the onions. Saute in the rendered beef fat until softened and aromatic, stirring, 2-3 minutes. Remove half the onions from the pan.

Place the seared brisket back into the pot, on top of the onions. Top with the remaining onions.

In a bowl, combine chili sauce, beef broth, wine, grape jelly, garlic, 1 ½ teaspoons kosher salt and ½ teaspoon black pepper. Mix well to combine. Pour the chili sauce mixture over the brisket and onions.

Cover the pot and place in the oven for 30 minutes. After 30 minutes, turn the heat down to 325 degrees. Cook for 3 ½ -4 hours, piercing with a fork to check if tender. Remove from the oven.

Allow the brisket to cool, then place in the fridge overnight.The following day, skim the hardened fat from the surface and slice the brisket. Slice it against the grain into desired thickness. Return all slices to the pot and either return the pot back to the fridge or if serving right away, reheat the pot over medium low heat until warm throughout.