Euonymus, 3 years in a pond basket with cat litter.
When I potted this little stick, 3 years ago I cut off ~95% of the roots, imagine a 1 cm thick CD. Today it was a solid block, 30x30x20 cm, of very ramified, fine feeder roots. Trunk diameter has grown from two to five cm in the same time. I cut the trunk and took the roots down to that CD size again and put it back in the basket but only filled it to 50%. now it's back to waiting another 2-3 years. Top will be worked in the meantime.