While visiting friends in New Jersey a few weeks ago, I saw my first walnut tree. But this was no ordinary walnut tree - it was the relatively rare, expensive black walnut. I peered at the fallen nuts but didn't touch them; the husks and shells yield an indelible dye (once used to dye clothing). Some of the husks were green, others dark brown. It's the shell inside the husk that's black. Be prepared to pay a lot for black walnuts at supermarkets. They're not just rare, they are also difficult to extract from their extremely hard husks. (Wood from the black walnut tree is valued for being extremely hard.) Their flavour is richer and more intense than that of ordinary varieties. A slight bitterness means they're good to use in desserts. Substitute them for ordinary walnuts (or other types of nuts) in brownies, chocolate-chip cookies, toffee, fudge, ice cream and muffins. For black-walnut pralines, cook soft brown sugar and cream to the soft ball stage (115 degrees Celsius). Add butter, then cool the mixture slightly. Add chopped black walnut, then beat until slightly grainy. Drop spoonfuls onto parchment paper, then cool until set.