Intervals of 400m or less on the track for a total of half an hour to an hour. Don't let HR get back to an easy level (120ish) before each next rep. Go as fast as you can get away with and still complete a ton of reps, and as far as you can get away with without injury.
For "aerobic" training, this beats any kind of tempo run, vo2max, whatever, because your true "aerobic" max occurs in the presence of a high anaerobic workload driving acidity in the muscles. This pH differential between blood and muscle increases the rate of oxygen and Co2 exchange between them. Done well, these workouts can get easier as you get a second wind halfway through.