How to Make It
Prepare the Brisket: Heat oil in a large skillet over high until just smoking. Sprinkle meat with salt and pepper. Cook in hot oil until browned on all sides, about 12 minutes total. Transfer to a 6- to 8-quart slow cooker; set aside.
Reduce heat under skillet to medium-high. Add onions to skillet. Cook, stirring occasionally, until browned and beginning to wilt, about 2 minutes. Add wine; cook, stirring and scraping bottom of skillet to loosen browned bits, until liquid is reduced by about half, about 2 minutes. Add to slow cooker. Place carrots, dried plums, thyme, and 1 cup water in slow cooker. Cover and cook on LOW until Brisket is tender, about 7 hours.
Prepare the Gremolata: Combine parsley, olive oil, horseradish, lemon zest, lemon juice, salt, and pepper in a food processor, and pulse until very finely chopped, about 10 times. Cover and refrigerate until ready to use.
Transfer Brisket to a cutting board to rest; transfer carrots to a platter. Pour cooking juices from slow cooker through a fine mesh strainer into a large bowl, discarding solids. Let strained liquid stand 10 minutes for fat to rise to the surface; skim and discard fat. Whisk liquid vigorously; transfer 1 1/2 cups to a small bowl. Discard remaining liquid. Slice Brisket against the grain; transfer to platter with carrots. Top with Gremolata, and serve with reserved liquid.