Preheat the oven to 350° F. Cut the apples into eight equal slices. Unwrap the crescent rolls and separate the triangles. Place a slice of apple on each triangle of dough on the wider side and roll up the dough into a croissant shape. Butter a 13x9–inch baking dish. In a separate bowl, combine the butter, cinnamon, sugar, and vanilla; mix until you get a liquid mixture without lumps and pour over the rolls. Pour Mountain Dew® between the rolls (but not over them) and bake for 35-45 minutes or until they become golden brown. Serve immediately with ice cream.