01 -
Pat the brisket dry with paper towels and season generously with salt and pepper. Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Sear the brisket for 4 to 5 minutes per side until deeply browned.
02 -
In the same skillet, add the remaining olive oil if needed. Lower heat slightly and sauté the sliced onions for 8 to 10 minutes until softened and starting to caramelize. Add garlic and cook for 1 minute until fragrant.
03 -
Add balsamic vinegar, brown sugar, Dijon mustard, Worcestershire sauce, and thyme to the skillet. Stir to combine, scraping up any browned bits. Pour in beef stock and bring to a simmer for a few minutes.
04 -
Place the seared brisket in the slow cooker. Pour the onion and sauce mixture over the meat, ensuring it is mostly submerged. Cover and cook on low for 8 to 10 hours or on high for 5 to 6 hours, until fork-tender.
05 -
Remove the brisket from the slow cooker and let it rest on a cutting board for 10 to 15 minutes. Slice against the grain into thick pieces.
06 -
For a thicker sauce, transfer the onion gravy to a saucepan. Stir in the cornstarch slurry and simmer over medium heat until thickened to desired consistency.
07 -
Arrange brisket slices on a serving platter and ladle the balsamic onion gravy over the top. Garnish with fresh herbs if desired.