Rub potatoes with ½ tablespoon oil; poke each several times with fork to vent. Bake potatoes on sheet tray at 400°F (375°F for convection) for 1 hour or until pierced easily with a knife; cool.
Finely chop 1 ounce Jarlsberg. Starting on top and approximately ½ inch from the sides of each potato, cut out an oval shape about ½-inch deep along the length of each potato. Leaving ¼-inch border inside each potato, scoop potato flesh and peel from each potato into mixing bowl; fold in chopped Jarlsberg, 3 ounces chèvre, sour cream, 1 tablespoon chives, salt and pepper. Fill potato shells with potato mixture. Bake potatoes at 350°F for 15 minutes (325°F for convection).
Heat remaining 1 tablespoon oil in a skillet over medium-high heat; add prosciutto and cook 2 minutes or until crisp, stirring frequently. Transfer to paper towel to drain. To same skillet, add mixed mushrooms; cook over medium heat 5 minutes or until mushrooms are tender and browned, stirring occasionally.
To serve, top hot potatoes with remaining slices of Jarlsberg, mushrooms, prosciutto, remaining 1 ounce chèvre and fresh truffles; sprinkle with remaining ½ tablespoon chives and salt.