Put the dried cranberries in a small bowl and cover with 1/2 cup of warm water. Set aside to plump for about 20 minutes.
Preheat the oven to 325°. In a medium saucepan, combine the milk, heavy cream, lemon zest, orange zest and 4 mint sprigs. Scrape the seeds from the vanilla bean into the milk and add the bean to the saucepan. Bring to a boil over moderate heat. Remove from the heat and stir for a few minutes to cool slightly. Whisk in the sugar and the gelatin and set aside for 3 minutes, then whisk again. Strain the mixture into a heatproof measuring cup.
Drain the cranberries and divide them among six 1/2-cup ramekins set on a baking sheet. Stir the milk mixture once and pour it over the cranberries, filling the ramekins. Top each with a challah round. Bake the puddings for 20 minutes, or until the custard is bubbling and still wobbly. Remove from the oven.
Preheat the broiler. Broil the puddings for about 30 seconds just to toast the bread rounds.
Let the custards cool, then refrigerate until completely set, at least 4 but not more than 6 hours.
Just before serving, melt the raspberry jam in a small nonreactive skillet over low heat. Run a knife around the inside of each ramekin to loosen the bread puddings and invert them onto dessert plates.
Spoon a little of the raspberry jam over and around them. Garnish each plate with a few mint leaves from the remaining sprig and serve.