Directions:

Roast:

1. Stir together first 4 ingredients, until a thick paste forms.
2. Preheat oven to 475˚ Season all sides of the roast well with salt and pepper. Place roast, bone-up, in a large, greased roasting pan. Roast on the bottom rack of the oven for 25 minutes, then pull out of oven and flip over so the bones are on the bottom.
3. Reduce oven temperature to 350˚ Wearing gloves or using a brush, coat top and sides with mustard mix. Roast for about 90 minutes more, rotating pan occasionally, until the internal temperature reaches 120˚F for medium-rare. Let rest, covered loosely with foil, for 30 minutes.
4. When time to serve, you can slice the bones off in one piece from the bottom, or slice in between the bones for thicker slices. Serve with the relish on the side.

Relish:

1. If using fresh cranberries, place in freezer until completely frozen.
2. Combine cranberries, sugar, salt, and pepper in food processor and pulse, scraping occasionally, until evenly, finely chopped. Add lemon zest and juice, then the horseradish and pulse a few more times, until evenly mixed.
3. Transfer to a serving dish and let rest in fridge for at least 1 hour. Keep cold in fridge until ready to serve.