On the 12th day of Christmas, former mile world record holder John Landy of Australia gave to me: a classic workout I've used with athletes for years, the 12-minute "up to you" fartlek. This workout is meant to break up 12 minutes' worth of fartlek however you choose. You can run 6 x 2 minutes, 1-2-3-3-2-1 minute, or even 1:45, 4:05, 45 seconds, 2:30, 1:00, 1:10, 15 seconds, and 30 seconds.
Gosta Holmer, the former Swedish national coach and developer of the fartlek would have loved this session for its simplicity and randomness. After each pick-up, recover based on feel and start the next pick-up whenever you feel inspired.
There you have it: the 12 workouts of Christmas. Just don't do them all in the 12 days before Christmas.