Following is a recipe for one of the mustard desserts, a spiced chestnut cream, from The Compleat Mustard by Rosamond Man and Robin Weir, which I wouldn't copy so directly if the book didn't happen to be out of print. We didn't taste this dessert at the tasting, I just rearranged the flavors so we could appreciate the combination and I could show everyone what mustard does to chestnuts (makes them taste like chocolate). At the tasting I just pureed candied chestnuts, dijon mustard, and a dash of cocoa powder and whipped it into mascarpone to inspire the cooks at the tasting to go explore (that's part of eating fearlessly), but the original recipe is:
8 oz chestnut puree
4 oz unsalted butter
4 oz sugar
2 teaspoons cacao
1 tablespoon mustard powder
1/4 pint double cream, whipped
6 fl oz cream, chilled, to serve
Heat the puree with the butter and sugar, stirring constantly until melted. Add the cacao and mustard powder and cook for a further 2 minutes. Remove the pan from the heat and leave to cool for 30 minutes.
Whisk in the whipped cream very thoroughly, then spoon into small bowls...and chill overnight. Serve with chilled cream handed round separately.
This could be altered in such a way as to use prepared mustard instead (I certainly would because I could then create dozens of variations on this by using different mustards). A prepared cognac mustard would do interesting flavor changes to that.