Doncaster notched nine tries in total as they ran out 61-14 winners at Cambridge, backing up in fine style their opening win over Hartpury at Castle Park a week earlier.
Dolly also kicked eight out of nine conversions in a strong performance.
Lock Evan Mintern got the ball rolling in the third minute before Billy McBryde crossed for the second.
Steve Boden’s men had to wait 13 minutes before their third and Dolly’s first, but they added two more before half-time through Dolly again and Connor Edwards as they built a 35-0 lead.
There was no let-up after the break as Dolly completed his hat-trick and Joe Margetts touched down, either side of a converted Cambridge response.
Margetts with his second and a score by replacement hooker Cam Terry completed the rout as the Knights continued their relentless start to the season in the second tier.