Place the seeds in a coffee grinder and grind to a powder. Place the mixture on a plate. Season the loin with salt and pepper to taste and dredge on all sides with the spice mixture.
Heat the oil in a medium skillet over high heat until almost smoking. Sear the lamb on all sides until golden brown. Transfer the lamb to the oven and roast for 8 to 10 minutes for medium-rare doneness. Remove and let rest.
Place the skillet on top of the stove over high heat. Remove all but 2 tablespoons of the fat. Add the shallots and cook until soft. Add the wine and cook until reduced by three-quarters. Add the stock and cook until reduced by half. Whisk in the mustards and season with salt and pepper, to taste. Remove from the heat and stir in the mint.
Serve with Braised Napa Cabbage with Red Wine Vinegar and Mint and Yukon Gold Mashed Potatoes with Green Garlic Butter.
Braised Napa Cabbage with Red Wine Vinegar and Mint:
Preheat oven to 400 degrees F. Place cabbage in a roasting pan, stir in the vinegar, honey, and chicken stock and season with salt and pepper. Cover with foil and roast in the oven until wilted, about 30 minutes. Remove from the oven and stir in the mint.
Yukon Gold Mashed Potatoes with Green Garlic Butter:
Place the potatoes in a large saucepan, cover with cold water, and add 2 tablespoons of salt. Bring to a boil and cook until soft. Drain well and place back in the pan over low heat. Add the cream and green garlic butter and mash until smooth. Season with salt and pepper, to taste.
Green Garlic Butter:
Place the butter, garlic, and herbs in a food processor and process until smooth. Season with salt and pepper.