Preheat the oven to <temperature>400<unit>°F</unit></temperature>

Line a medium loaf pan with parchment paper, cut to fit and cover the sides

Peel <quantity>3</quantity> sweet potatoes

Thinly slice them with a mandoline and transfer to a bowl

Add <quantity>2<unit>tbsp</unit></quantity> of duck fat

Add <quantity>3<unit>tbsp</unit></quantity> of maple syrup

Roll <quantity>2</quantity> nori sheets. Cut them into thin strips and add to the sweet potatoes. Mix to combine

Add salt to taste and mix to combine

Layer the sweet potato mix in the pan and pour over any remaining liquid. Cover the potatoes with another piece of parchment paper

Bake the sweet potatoes for 30m until they begin to blister

Add <quantity>1<unit>tbsp</unit></quantity> of coriander seeds and <quantity>1<unit>tbsp</unit></quantity> of cumin seeds to a mortar

Add <quantity>1<unit>tbsp</unit></quantity> of dried lavender and <quantity>1<unit>tbsp</unit></quantity> of salt

Crush with the pestle to obtain a coarsely ground powder

Remove the silver sinew on the flesh side of <quantity>3</quantity> duck breasts. Turn to the skin side and trim the excess fat from the sides

Score the skin of the duck breast in both directions with a knife. Avoid scoring too deep so that you do not pierce the meat

Rub <quantity>1<unit>tbsp</unit></quantity> of honey on each duck breast, starting on the skin side

Rub the spice mix to taste on both sides of each breast

Remove the sweet potato from the oven and press another loaf pan on top of it. Let it cool down on the counter

Raise the oven temperature to <temperature>425<unit>°F</unit></temperature>

Transfer the breasts to a roasting pan. Roast for 10m until the fat on the skin has rendered and is slightly colored. Remove from the oven

Let the breasts rest for 15m to continue to cook internally. Turn the oven to broil on maximum heat

Transfer the potatoes to a cutting board, holding them by the bottom paper. Cover them with a clean parchment paper sheet. Flip them carefully and remove the paper on top

Return the duck to the oven for 4m to brown and make the skin crispy

Let it rest for 3m to set the juices

Slice the gratin into rectangles and reheat in the oven for 2m to serve. The sweet potato & nori gratin is ready

Cut the breasts in half lengthwise

Transfer half of the breast to a serving board, slice it and arrange in the board

Plate a piece of the gratin on the side

The roast duck breast & sweet potato gratin is ready. Enjoy!