Prepare the Brine: Add water, cooking salt, and curing salt to a large container. Stir until dissolved. Set aside.
Toast Spices for Brine: Toast coriander seeds, chilli flakes, mustard seeds, juniper berries, cloves, and cinnamon sticks over medium heat. Add to the saltwater mixture with smashed garlic cloves and bay leaves.
Brine the Brisket: Submerge trimmed brisket in brine, cover, and refrigerate for 10 days, flipping every 2-3 days.
Rinse Brisket: Remove brisket from brine, rinse under cold water, and pat dry.
Prepare Pastrami Spice: Toast black peppercorns, coriander seeds, and mustard seeds. Crush lightly and mix with brown sugar, smoked paprika, and garlic powder.
Season and Smoke: Season brisket with spice mixture. Smoke at 120°C (250°F) until internal temperature reaches 65°C (150°F).
Steam in Oven: Place smoked brisket in an oven tray with water. Cover and steam at 160°C (325°F) until internal temperature is 94°C (200°F).
Rest and Serve: Let brisket rest for 10-15 minutes before slicing and serving.