Drive 300 miles on Bathurst in the #10 Holden Xbox Racing Team Commodore VF.
This is likely best done in Free Play with no drivatars, although it can be done in any mode that permits the required vehicle on Bathurst. Ensure that you have the correct track (Bathurst is the Mount Panorama Circuit in Australia) selected and choose the #10 Holden Xbox Racing Team Commodore VF. You do not have to complete this in one session and if you are in Free Play, you don't have to have any opponents. You can track your relative progress toward this achievement by looking at the red line at the bottom of the grey achievement picture in the achievement app on the Xbox One.
The #10 Holden Xbox Racing Team Commodore VF is an S class vehicle by Holden that is available in the Purchase Cars screen. If you have not purchased the DLC that includes the vehicle, you will be prompted to do so. You can purchase this vehicle solo or as part of the Top Gear Car Pack. The vehicle will cost you zero credits in-game.