Score the Duck Breasts: With a sharp knife, carefully score the skin of each duck breast in a crisscross pattern, spacing the cuts about ½ inch apart. Avoid cutting all the way through the fat into the meat.
Season and Marinate: Combine the garam masala, salt, pepper, and allspice in a small bowl. Rub this mixture evenly over the duck breasts, covering all sides. Wrap the breasts loosely in plastic wrap and let them marinate at room temperature for 30 minutes.
Preheat Your Oven: Set your oven to 350°F to prepare for finishing the duck.
Sear the Duck Skin: Heat a large skillet over medium heat. Place the duck breasts in the skillet, skin-side down. Cook for 4–5 minutes until most of the fat has rendered out and the skin becomes deeply golden and crisp. Flip the breasts over and sear the flesh side briefly for about 1 minute.
Start the Sauce: Drain off most of the rendered fat from the skillet, leaving just a thin coating. Add the diced plums (or cherries, if using), the wine, and the bay leaf to the pan. Turn the duck breasts skin-side up again, and transfer the skillet to the preheated oven.
Cook to Temperature: Roast the duck breasts in the oven for 3–5 minutes, or until the internal temperature reaches 125°F when measured with an instant-read thermometer. This will yield medium-rare doneness.
Rest the Duck: Remove the duck breasts from the skillet and transfer them to a cutting board. Let the meat rest for 5 minutes to allow the juices to redistribute.
Finish the Sauce: Place the skillet back on medium-high heat. Let the plums and pan juices simmer for 2–3 minutes, stirring occasionally, until the sauce thickens slightly. Add a drizzle of balsamic vinegar and toss in the chopped fresh basil leaves for added flavor.
Slice and Serve: Thinly slice the duck breasts and arrange them on a serving platter. Spoon the warm plum sauce over the duck slices and serve immediately.