Season duck breast with salt and pepper on both sides. Add duck breast skin side down to a cold cast iron pan. Turn heat up to medium high and sear for about 3 minutes, or until the skin is a nice golden brown. Turn duck flesh side down and sear for 1 minute. Flip back onto its skin and put the cast iron into the pre-heated oven for 8 minutes. Remove duck from the oven and let rest on a cutting board for 10 minutes. Reserve duck fat for croissant grilled cheese.
To make the sauce, add onion, garlic and ginger to a small saucepan and cook on medium high heat for about 5 minutes. You want to see the onions start to bring on some colour. Add hoisin, vinegar, ponzu, sesame oil and blueberry jam and stir to combine. Turn heat down to medium and continue to cook until it has reduced and become thick and sticky.
Once the duck has had time to rest, slice the duck very thin and add it to the sauce. Mix the duck into the sauce and set aside.
Time to make the croissant grilled cheese. Each duck sandwich requires two croissant grilled cheeses.
Slice each croissant in half, and place a few slices of the cheese in between each half. Place cast iron on stove top and turn the heat to medium high. Add a teaspoon or so of the duck fat to the pan. Cook grilled cheese for a few minutes per side, ensuring you press down on the sandwich so it flattens quite a bit.
To assemble layer a few good spoonful’s of the duck hoisin mixture onto one flattened grilled cheese. Top with another grilled cheese and enjoy! Napkins will be required!