Preheat oven according to instructions on pastry pack. Pull off mangold leaves, wash, cut out white stalks and chop the remaining leaf green into bite-sized pieces. Slice the apples and onions. Roll out the puff pastry onto the baking tray according to the instructions on the pack, spread on crème fraîche and arrange sliced apple, mangold and onions on top. Pop into the oven and bake. While the tart is in the oven, peel the kohlrabi and cut into fine sticks, wash the orange well and cut off the zest. Combine and season with vinegar, oil, honey, salt and pepper. Stir well and serve with the apple-and-mangold tart.