If you wish to obtain this during Career mode like I did then you need to do the following:
1) In the Racing Series, complete Prototype 1 Racing to unlock the 3 bonus races.
2) Race the (Full Circuit at Le Mans) making sure you finish at least 3rd to get a Gold.
3) Achievement will pop once the race is over.
Whichever car you use for the Prototype 1 Racing Championship should get you the achievement.
If you vote negative please state why so I can improve the guide....
Thanks.