In a medium saucepan, combine the paprika, vanilla, apple cider vinegar, tomato paste, honey, sugar and mustard.
Bring to a gentle simmer and cook, stirring, for 5 minutes or until thickened. Remove from the heat and add in the bourbon and liquid smoke. Stir to combine and set aside to cool.
Place the brisket, in a large roasting pan. Add in the leeks, bay leaves, thyme, peppercorns, water, vinegar and BBQ sauce.
Cover with aluminium foil and roast for 4 hours or until fork-tender. Strain out the liquid from the pan and reserve, discard the solids.
Place the drippings in a large pot over medium-high heat and cook until reduced.
Place the brisket back in the pan and baste with the remaining BBQ sauce. Increase the oven temperature to 390°F and roast until caramelised, approximately 20 minutes.