Special equipment: a 10-inch deep-dish tart pan with a removable bottom
In a food processor, process the vanilla wafers to crumbs. Pour in the melted butter and pulse until the crumbs are moistened.
Press the crumbs into a 10-inch deep-dish tart pan to line the bottom and sides. Refrigerate for 10 minutes.
In a medium bowl, whisk together the egg yolks, 1/4 cup of the sugar and the cornstarch. Set aside.
In a small bowl, mix the gelatin with 2 tablespoons cold water. Set aside.
In a medium saucepot, combine the milk with another 1/4 cup of the sugar and the vanilla bean. Bring to a boil over medium heat, whisking occasionally.
A ladleful at a time, slowly pour the heated milk into the egg yolk mixture, whisking to temper the yolks. When half of the milk has been added, pour the hot egg mixture back into the saucepot, whisking constantly. Heat over medium heat, whisking constantly, until thickened and bubbles start appearing on the surface.
Whisk the bloomed gelatin into the custard. Pour the custard through a fine-mesh strainer to remove any lumps or overcooked yolks.
Pour the strained custard into the tart shell and refrigerate for 1 hour, until set.
In a small saucepot, bring the orange juice and the remaining 1/2 cup sugar to a boil. Add the dried orange slices and simmer until syrupy, 10 minutes. Set aside to cool; the orange slices will continue to soften.
Remove the tart from the refrigerator and decorate with the orange slices in a fan pattern. Drizzle the tart with some of the orange syrup.
Place the tart back in the refrigerator for another hour, or until the candied oranges are set.