Place the duck skin side up. Using a sharp knife, score 4 (1/4-inch-deep) cuts across the skin at a 45 degree angle. Sprinkle 1/4 teaspoon salt and 1/4 teaspoon pepper over the meat side of each duck breast.
Heat a well-seasoned skillet or nonstick pan over high heat. When pan is hot, add duck breasts, skin side down, and cook for 5 minutes, or until skin is brown and crispy. Flip and cook for 2 more minutes. If you are unfamiliar with duck breasts, don't be put off by their unusual look. The fat-to-meat proportions reverse themselves when cooked, as much of the fat is rendered and the meat expands.
Remove pan from heat (save the drippings) and transfer duck breasts, skin side up, to a cooking sheet lined with aluminum foil. Bake on the top rack of the oven for 6 minutes.
Carefully discard all but 2 tablespoons of duck drippings from the pan. Return pan to medium heat and add shallot. Stir occasionally for 3 minutes, or until shallot begins to turn golden. Add Cassis to the pan and stir with a wooden spoon to loosen up the browned bits left by the duck. Add jam, vinegar, and remaining teaspoon of black pepper, and stir occasionally for 3 minutes. Remove from heat.
Remove duck from the oven and slice each breast at a 45 degree angle into 1/4-inch-thick strips (properly cooked duck should resemble medium-rare steak). Arrange in a fanlike pattern on a warmed plates and spoon Cassis compote overtop. Serve immediately.