I would do:
30 seconds of constant tension effort / 30 seconds of rest x 3 (so 30/30 rest/30/30 rest/30) this is ONE set. Rest 2-3 minutes do another bout, rest 2-3 minutes and do a 3rd bout.
The key is how you do the reps. You want the muscles to be under constant tension. The "allowed" range of motion is from parallel to about 2" before lockout.
What you want to do is spend time in that range... you can do reps over the full allowed range, partials, holds, doesn't matter as long as you stay in the range for 30 seconds. And the movements should all be under control no momentum. Start lighter than you think.
Or you can do a mechanical drop set like this... sets of 8-8-8 for strength-endurance GPP.