01 - Preheat oven to 300°F.
02 - Pat brisket dry and rub with salt, pepper, smoked paprika, garlic powder, and onion powder.
03 - In a large oven-safe pot, heat olive oil over medium-high heat. Sear brisket on all sides until browned, about 3–4 minutes per side.
04 - Remove brisket. Add sliced onion and smashed garlic to the pot; cook for 2 minutes. Return brisket to the pot, add beef broth, cover tightly with lid or foil.
05 - Transfer to oven and cook for 4–4.5 hours, until the brisket is fork-tender.
06 - While the brisket cooks, prepare BBQ sauce: In a saucepan, combine ketchup, apple cider vinegar, brown sugar, Worcestershire sauce, Dijon mustard, smoked paprika, and chili powder. Simmer on low heat for 15 minutes, stirring occasionally. Season with salt and pepper. Set aside.
07 - For the slaw, combine green and red cabbage and carrot in a large bowl. In a small bowl, whisk mayonnaise, apple cider vinegar, Dijon mustard, honey, salt, and pepper. Toss with vegetables to coat. Chill until ready to use.
08 - Remove brisket from oven and let rest for 20 minutes. Shred meat using two forks, discarding excess fat. Mix with half the BBQ sauce (reserve remaining sauce for serving).
09 - Brush slider buns with melted butter and toast lightly in oven or skillet.
10 - Pile brisket onto bottom buns, drizzle with extra BBQ sauce, top with slaw, and place bun tops. Serve immediately.