Through the feed opening of a running blender add, 1 at a time, the vinegar, shallots, tarragon, rosemary, kosher salt, black pepper, and olive oil to form a paste. Rub this into the rabbit loin and let sit for 2 hours.
Preheat oven to 375 degrees F.
Heat 2 tablespoons olive oil over medium heat in a saute pan with oven safe handles, and sear marinated rabbit on all sides. Transfer to oven, cover and let cook until it reaches an internal temperature of 135 degrees F, about 20 minutes. Remove and bring to room temperature, then chill.
Using a 2-inch circle cutter or biscuit cutter, cut the mini potato rolls into rounds and lay out on a utility platter.
Heat oil over medium heat in a saute pan and add the shiitakes, onions and garlic. Saute until shiitakes are tender and onions are translucent. Add demi-glace and balsamic vinegar, and stir to combine. Transfer to a food processor and pulse to make a coarse hash.
Slice rabbit into thin slices. Spread some hash on each potato roll and top with thin slices rabbit. Drizzle sour cream sauce over, then garnish with chopped tarragon and orange segments.