4 – 5 x 800m @ you choose the effort. 10k? 5k? Mix it up. Run #2 and #4 hammering the last 400m of the 800m interval. (Or run them all at 10k pace; hammering the last 400 2 out of 4 intervals).
Example: do 1 x 800m @ 10k; 1 @ 5k; 1 @ 10k; 1 @ 5k
2 min. recovery jog b/n repeats.
Go with how you feel.