Go to free play - rent or buy the 2015 Lotus E23 - select track spa in the rain - game options - laps 1 then press
to save the settings - and then start and complete the race (No drivatars needed)
EDIT: As ScuzzyBunny pointed out in the comments you can also get this in a private multiplayer 30sec. Timed race
EDIT: As T4llboy pointed out in the comments the track is called Circuit de Spa-Francorchamps when selecting a track