Try
6lbs of Dark DME
Steep:
.25lb roasted barley
1lb chocolate malt
.5lb 120L Crystal Malt
1oz Kent Goldings 60 min boil
.5oz Kent Goldings 30min boil
Add 4tablespoons of 100% cacao (chocolate) powder and 1 cup lactose at 10minutes left in the boil.
If its not chocolaty/sweet enough when moving to secondary, boil up a pint of water and some more cacao and/or lactose
To get a head like Young's you would have to keg with a N2/CO2 gas mixture.
Should be pretty good, off the top of my head. What do you guru's think? I could be off with the Dark DME, never used the stuff so it may not be good to use completely... but I think it would be alright.