This is unlocked by rolling your vehicle 5 times in one race. I found the simplest race for this to be Buggy - Siberia 2. If you take the Beetle buggy you will roll easily coming down the mogul hill and make sure to hit the single snow mound in the frozen river. Its 4 laps so as long as you can get a roll in the moguls (or a double roll off the big mound) you're golden!