Heat 1 tablespoon of the oil in a medium saucepan over medium-high heat. Add the shallots, carrot, celery, and garlic, reduce the heat, and saute until the vegetables are soft and beginning to brown, about to minutes. Pour in the wine, bring it to a boil, then lower the heat and simmer until reduced by half, about 30 minutes. Add the blueberries and simmer for 15 minutes, then add the chicken stock and simmer for another 15 minutes. Strain, pressing on the solids to squeeze out any remaining liquid before discarding them. Whisk in the butter a little at a time. Add the honey and sage and let sleep over very low heat for 10-15 minutes, then remove the sage. Season with salt and pepper to taste, and keep the sauce warm. --Rub the crushed juniper berries onto the venison along with generous amounts of salt and pepper. Heat the remaining 2 tablespoons of oil in a large pan over high heat until just smoking, then add the venison, searing it well. Cook for about 3 minutes per side, or until barely medium-rare. (Poke the meat with a finger to check its doneness; if it springs back, it's ready.) Remove the tenderloin from the heat and let it sit, covered loosely in foil, for 5 minutes, then slice into medallions. Spoon the sauce over them and serve. Serves four.