I can't really speak for you, but I know when I did 20 rep squats once a week, years ago, it really crippled me for days. Almost going up stairs using my hands as well as feet. Bending down to get a pencil off the floor, took 3 full minutes (Ha ha)
I am not sure if I was going to hard just once per week, then waiting until the next week again. It seemed to really get better, (and I made as good or better progress), using a little more frequency (2nd lighter workout) thru the week along with the heavy one and getting deads in as well. It seemed to aid recovery and I was closer to being adapted to them.
As far as supplements I might say magnesium, but I would only be guessing.
I know guys might also add foam rolling, massage etc. and or just BW squats too, thru the week, to aid in more circulation and thus helping the soreness dissipate.