Using a spice grinder or mortar and pestle, crush the black peppercorns, coriander seeds, and mustard seeds until coarse.

Transfer to a small bowl and mix with the ground black pepper, ground coriander, brown sugar, smoked paprika, garlic powder, and kosher salt.

Pat the brisket dry. Using a sharp knife, score the fat cap in a shallow crosshatch pattern.

Brush the brisket all over with the deli mustard, coating all sides evenly.

Press the pastrami spice rub firmly into the brisket, making sure it’s fully and evenly coated.

Wrap the brisket tightly in two layers of heavy-duty aluminum foil, sealing well so no liquid can escape.

Place the wrapped brisket fat-side up on a baking sheet.

Roast at 300°F for 4 hours.

Carefully snip a small hole in the foil and drain off any excess rendered fat and liquid.

Rewrap the brisket tightly and refrigerate until fully chilled, at least a few hours and up to 2 days.

Reheat the brisket, still wrapped in foil, at 325–350°F for about 30 minutes, until completely warmed through.

Unwrap the brisket and brush the fat cap with the honey.

Broil until deeply browned and blackened in spots.

Rest briefly, then slice against the grain and serve.

Make sure the brisket is fully heated before broiling so the exterior doesn’t burn before the inside is hot.