Step 1

Marinate the beef: Stir all the ingredients except the beef together in a large saucepan. Bring to a boil over medium-high heat, then remove from the heat and cool completely.

Step 2

Place the beef in the bowl of a 6-quart or larger slow cooker and pour in the cooled marinade. (The meat will not be completely submerged.) Cover and place the bowl in the refrigerator to marinate for 2 days, flipping the meat once or twice per day.

Step 3

Slow-cook the beef: Remove the beef from refrigerator about 30 minutes before cooking. Transfer the meat to a large plate and pat completely dry with paper towels. Do not discard the marinade. Generously season the meat all over with the salt and pepper.

Step 4

Heat the oil over high heat in a large cast iron or heavy-bottomed skillet until shimmering. Add the beef and sear each side until deeply browned, 4 to 5 minutes per side.

Step 5

Return the beef to the marinade in the slow cooker. Cover with the lid. Cook until the beef is tender and cooked through, 8 to 9 hours on LOW, or 5 to 6 hours on HIGH. Transfer the beef to a cutting board and rest for about 5 minutes.

Step 6

Meanwhile, strain the cooking liquid through a strainer or colander set over a bowl. Measure out 2 cups of the liquid and set aside (discard the remaining cooking liquid and solids).

Step 7

Melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook, whisking constantly, for 1 to 2 minutes. Gradually whisk in the 2 cups reserved cooking liquid. Cook, whisking frequently, until thickened, 3 to 4 minutes. Slice the meat and serve hot.