In a large sautÚ pan bring the oil to medium heat. Season the breast halves with salt and pepper and cook slowly in the sautÚ pan, skin side down, until the fat is rendered and the skin takes on a rich, brown color. After 10 to 12 minutes turn the breasts and cook for 3 to 4 minutes.
Remove the breasts, pat dry, and reserve on a warm platter. Add the stock, cider and juniper berries to the sautÚ pan over high heat and reduce by half, scraping the pan all the while. Reduce the heat, whisk in 2 tablespoons butter and remove from heat. Allow the sauce to stand until needed, then strain and ladle over the duck when serving.
Peel, seed and thinly slice the apple into ten semi-circle pieces. In a sautÚ pan melt the remaining butter and add the vinegar. Heat through. Soften the apple pieces in the butter and vinegar mixture for 3 or 4 minutes, until the apples are soft but not crumbling.
To serve, slice the breasts, arrange the apples beside each portion, and spoon the sauce over the duck and apples.