Having already wrapped up the league title a month earlier the double was acheived courtesy of Luke Palmer
's eighty ninth minute spot kick.
Manager John Winter had to reshuffle his pack due to a combination of injuries and unavaialblity which ruled out Aysa Corrick, Lloyd Halliwell and joint top scorer Danny Carter.
The depth of the squad was highlighted as Mangotsfield produced some free flowing passing football on a slick playing surface.
In a final of few chances Ashton & Backwell's only notable chance came on twenty five minutes when Kane Mannings was called into action, tipping the ball over the bar for a corner.
With Mangotsfield enjoying the better of the first half the clearcut chances fell to the league champions.
The best of these fell to Luke Palmer
who was twice put through by the inventive Louis Ross only for goalkeeper Sean Byrne to prevail on both occasions.
The second half continued in similar vein with Mangotsfield carrying the greater threat. Midway through the half a Jake Slocombe header hit the bar and later on Omar Lindsay had a header cleared off the line.
With the match seemingly heading towards extra time Mike Baker's through ball sent Luke Palmer
away only to be brought down by goalkeeper Sean Byrne.
After picking himself up and with just a minute of the ninety remaining Palmer drilled the spot kick home for his third of the season to earn Mangotsfield a deserved victory.
After the victory Manager John Winter told MUFC Online "I've had a great bunch of lads whose efforts over the past two years have been tremendous and I'd like to congratulate each and every one of them on their achievements.
Winter added "I'd also like to give a special mention to my assistant Wayne Morris for his support and knowledge of football at this level which has been invaluable."
Line up : 1. Kane Mannings, 2. Mayson Evans, 3. Jacob Morris, 4. Omar Lindsay, 5. Harry Greenland, 6. Mike Baker, 7. Louis Ross (12. Tom Shopland 75'), 8. Jake Slocombe, 9. Jack Withey, 10. Jack Winter (15. Scott Jenkins 60'), 11. Luke Palmer
Substitutes : 12. Tom Shopland, 14. Warren Smith, 15. Scott Jenkins, 16. Keiron Clark, 17. Mitchell Craddock.
Bookings : 3. Jacob Morris, 5. Harry Greenland.