With a paring knife, score the duck breast, in a cross-hatch pattern, to a depth of about 1 inch (2.5 cm); season both sides with salt and pepper. Heat a cast iron pan to high, add a bit of oil and sear the duck breast, skin down, for 5 to 6 minutes, until nice and crispy, then turn and continue to sear for another 4 to 5 minutes; remove from the pan and allow to rest.
Deglaze the pan with apple cider and grainy mustard, add apple, green onions and blueberries; let simmer for 3 to 4 minutes until the apple starts to soften.
To plate, slice the breasts and top with apple and blueberry sauce. Makes 2 servings.