For the brisket: Sprinkle the brisket evenly all over with the crushed peppercorns and 1 tablespoon salt; firmly press into the meat. Heat the oil in a 6-quart Instant Pot® set to saute mode (see Cook's Note) until shimmering. Add the brisket and cook, turning occasionally, until browned all over, about 8 minutes. Add the garlic and broth then follow the manufacturer's guide for locking the lid and preparing to cook. Set to pressure cook on high for 1 hour 15 minutes.

After the pressure-cook cycle is complete, follow the manufacturer's guide for quick release and wait until the quick-release cycle is complete. Being careful of any remaining steam, unlock and remove the lid. Transfer the brisket to a cutting board to rest for 10 minutes before slicing thinly across the grain and then cutting into bite-size pieces. Pour the cooking liquid into a large liquid measuring cup and skim off the fat; reserve the liquid for the barbecue sauce.

For the slaw: Meanwhile, combine the mayonnaise, sour cream, Dijon, vinegar, honey and celery salt in a medium bowl and whisk well. Add the broccoli slaw, toss to combine and season with salt and pepper. Cover and refrigerate until ready to serve.

For the barbecue sauce: Return ½ cup of the reserved cooking liquid to the Instant Pot. Add the ketchup, vinegar, mustard, brown sugar, Worcestershire, molasses, celery salt and ½ teaspoon salt and set to saute mode. Bring to a boil and cook, stirring frequently, until reduced slightly, about 5 minutes. Add the sliced brisket, gently toss to coat, bring the sauce to a boil then immediately turn off the heat.

For serving: Split the slider buns. Put some slaw and brisket on each bottom bun. Top with more slaw and close the sliders with the top buns.