Bloom the gelatin by sprinkling it over 1 cup of the duck stock in a small mixing bowl – being sure to dissolve all of it. If the stock is gelatinous heat it slightly to bring it to a more watery consistency. Once the gelatin is dissolved place the bowl over a pot with simmering water in it and heat the mixture until it becomes clear. Mix in the apple cider vinegar and salt, to taste. Refrigerate until needed.

Note: Depending on the richness of the stock used, the vinegar to stock ratio may need to be adjusted. The important thing is to keep the liquid (vinegar and stock) to gelatin ratio the same as it is in this recipe.

Heat the oven to 375 degrees F.

Heat a nonstick saute pan over medium heat and lay in the duck breasts, skin side down. Reduce the heat to low once the fat starts to melt and cook the breast very slowly for about 30 minutes to render as much of the fat as possible. Increase the heat if needed so that the final product is a rendered duck breast with a golden brown skin side. Flip the breasts over in the pan and roast for 3 to 8 minutes (depending on the size of the breast) until medium rare. Let the breasts cool at room temperature and then refrigerate.

Increase the oven to 400 degrees F. Peel the apples and slice them thin (about 1/8 inch) on a mandolin. Line 2 half-sheet pans with parchment paper. Toss the apple slices with oil and salt and pepper. Spread out on the sheet pans and roast until the apples are barely cooked through – still slightly crispy on the inside. Let cool at room temperature.

Cut the stems off the beet greens so that only leaves remain. Boil a small pot of salted water. Prepare an ice bath in a medium size bowl. Blanch the beet greens in the boiling water by submerging them completely for about 10 to 15 seconds. Spoon them out and plunge them in the ice bath. Set the greens out individually on paper towels to dry. Layer the towels several times if necessary.

When the duck breasts have fully cooled slice them lengthwise into thin slices – less than 1/8-inch thick. Soak the slices in the orange juice.

Warm the aspic in the mixing bowl over simmering water.

Line 2 small triangular terrine molds with plastic wrap. Layer beet greens over the plastic wrap to cover the inside of the terrine mold completely and leave overhang on the edges to fold over the top. Brush the greens liberally with aspic. Layer the sliced apples and brush liberally with aspic. Put down another layer of beet greens and brush with aspic. Set in a layer of sliced duck. Layer as much as needed so that the terrine molds are full. Be very liberal with the aspic. It is the glue that holds the terrine together. When the mold is full fold the plastic over the top and put on the lid – pressing down to work out any air pockets. Use cans or anything else you have around the kitchen to put weight on the terrines while refrigerating.

When the terrines are fully chilled remove them from the refrigerator. Turn them out onto a cutting board, using the plastic to pull it carefully from the mold without breaking them. Carefully slice each terrine into 8 portions. Lay them out on a sheet pan. Heat the remaining aspic (if any) and use it to glaze the faces of the terrine slices. Refrigerate until ready to serve. It's important to keep these cold until service, as they will become very difficult to plate when the aspic begins to warm.