Heat oven to 250°F.
Whiz the peppercorns, juniper berries, and mustard seeds in a spice grinder and add to the rest of the rub ingredients. Reserve about a quarter of the rub for the gravy.
Stab the roast (not too deeply) and thoroughly rub the above mix into the roast, covering entirely.
Truss the roast to be as round as possible.
Place a rack in the middle of a cookie sheet and place the roast on the rack. You want a rack that will hold the roast above the edges of the cookie sheet.
Place the probe end of the thermometer into the middle of the roast and set for 130-134°F, depending on how done you want the roast.,
Cooking time will be APPROXIMATELY 30 minutes per inch (of diameter). So a 4 inch around roast, will take around 2 hours.
When the roast reaches the desired internal temperature, remove from the oven for a minute, and turn on the broiler to high. Once ready, pop the roast in and broil for 5 minutes, flip over and broil for another 5 minutes.
Remove the roast from the oven, place on cutting board, cut off the trussing, and slice. No need to rest!