I've kept my imperial chocolate stout continuously on tap for years. It's always been a hit, even with folks that aren't beer drinkers.
Here are the basics for five gallons:
16 lb 2 row pale malt (I prefer Golden Promise)
1 lb flaked barley
1 lb chocolate malt
1/4 lb black barley malt
1/4 lb black patent malt (could combine both black malts into either one really)
1/4 lb roasted barley
1/2 lb crystal/caramel malt 40-60L
1/2 lb caramalt
1/4 lb Gambrinus Honey Malt
2 oz Chinook pellets, 60 minutes
2 oz Cascade pellets, 15-20 minutes
2 lb honey, end of boil (TURN OFF THE BURNER BEFORE STIRRING IN!)
1/2 lb low fat cocoa powder, end of boil
Fermentis S04, 2 packs
1/2 lb cacao nibs and a scraped and smushed vanilla bean, soaked in dark rum for a week, then add the whole thing at secondary
1 oz pure chocolate extract, add at kegging
I have been mashing this at 148°F to get the FG down in the mid-upper 20s.
Serve on nitro if possible!
Cheers!