Allow the leftover brisket slices to warm on the counter while you preheat the oven to 325 degrees.u003cbr/u003eu003cbr/u003ePlace the slices in a pan with some liquid, either beef broth or more apple juice, and cover tightly in a double layer of foil. This keeps everything nice and juicy while allowing it to heat evenly throughout.u003cbr/u003eu003cbr/u003eCook until warmed through, about 15 to 20 minutes.