Set a 1-quart saucepan over medium-high heat and add the olive oil. Once the oil is hot, about 30 seconds, add the shallots, garlic and cherries. Cook the shallots, garlic and cherries until the garlic is fragrant and the shallots begin to caramelize, about 1 minute. Deglaze the pan with the vinegar, and when the vinegar is almost completely reduced, about 3 minutes, add the stock and chopped sage. Bring the sauce to a boil, reduce heat to a simmer, and cook for 15 minutes. Once the sauce is cooked, swirl the cold butter into the sauce and season with salt and pepper, to taste.
Place the haricots verts in a 10-inch saute pan and cover with 1 cup of water. Season with salt and pepper and place the butter in the pan. Bring to a boil over high heat. Cook until crisp-tender, 6 to 7 minutes.
Place the potatoes in a saucepan and cover with water. Set over high heat and bring to a boil. Cook the potatoes until tender, about 7 to 8 minutes. Remove from the heat and cool under running cold water. Once cool enough to handle, place the potatoes on a cutting board and slice in half lengthwise. Season the potatoes with salt and pepper, to taste. Heat a 10-inch saute pan with the reserved duck fat over medium high heat. Place the potatoes, cut-side down, in the pan and cook the potatoes until browned and crispy, about 3 minutes. Turn over and cook for another 3 minutes. Remove from the pan and serve with the duck.
To serve the dish, divide the haricots verts evenly between 4 warmed entree plates. Place 4 fingerling potato halves on each of the plates, and 6 slices of the duck breast fanned out along the plate. Drizzle about 1/4 cup of the sauce on each plate and serve garnished with fresh or fried sage leaves.
Preheat the oven to 400 degrees F.
Score the duck breasts on the fatty side using a sharp knife, cutting about 1/8-inch into the skin in a cross hatch pattern. Heat a 12-inch saute pan over medium-low heat. Season the duck breasts evenly on both sides with the salt and pepper, and place, skin side down, in the hot skillet. Cook the breast until the skin is crispy and most of the fat has rendered, about 10 to 12 minutes. Pour off the fat from the pan and reserve 2 tablespoons of it on the side. Turn the breast over, and place in the hot oven for 10 minutes. Remove from the oven, allow to rest for 3 minutes, and slice each breast into 12 slices. Serve while hot.