Pull the excess fat from the cavity of the duck.

Freeze the fat for later use.

Combine grapefruit juice, grapefruit zest, blood orange juice, blood orange zest, soy sauce, miso, sambal oelek, sesame oil and salt in a bowl and whisk until smooth to create the marinade.

Place the duck in a large bowl and pour the citrus-soy marinade over it.

Cover and marinate the duck for 1 hour in the refrigerator.

Preheat the oven to 300F.

Remove the duck from the marinade and place it on a rack in a roasting pan.

Poke the skin all over the duck with a skewer or the tip of a small knife.

Place the blood orange quarters, chopped red onion, garlic cloves and fresh thyme in the duck's cavity.

Tie the legs together with butchers twine.

Roast the duck for 1 hour, removing rendered fat periodically.

Strain and freeze the rendered fat.

Increase the oven temperature to 450F and roast the duck for another 45 minutes, basting every few minutes with the marinade.

If the duck is burning, lower the heat to 350F.

The duck is done when the legs move easily and an instant-read thermometer inserted into the thickest part of the thigh registers 160F.

Let the duck rest on a cutting board for 30 minutes before carving.