1To prepare the custard:
2Combine the milk and cornstarch in a bowl; blend until smooth. Whisk in the whole egg and yolks, beating until smooth.
3Combine the cream, vanilla bean and sugar in a saucepan and carefully bring to a boil. When the mixture just boils, whisk a ladleful into the egg mixture to temper it, then whisk this back into the cream mixture.
4Cook, stirring constantly, until the mixture is thick enough to coat the back of a spoon. Strain the custard and pour into 8 large custard cups. Refrigerate to chill.
5To prepare the chiffon cakes:
6Preheat the oven to 325°F. Spray 8 molds with nonstick cooking spray.
7Sift the cake flour, sugar, baking powder and salt into a large bowl. Add the oil, egg yolks, orange juice, zest and vanilla. Stir until smooth, but do not overbeat.
8Beat the egg whites until frothy. Add the cream of tartar and beat until soft peaks form. Gently fold the beaten whites into the orange batter.
9Fill the sprayed molds nearly to the top with the batter.
10Bake approximately 25 minutes, until the cakes bounce back when lightly pressed with your fingertip.
11Remove from the oven and let cool on a wire rack. When completely cool, remove the cakes from the molds. Cover the cakes to keep them moist.
12To prepare the glaze:
13Chop the chocolate into small pieces.
14Place the butter in a saucepan and heat until it is just about to bubble. Remove from the heat; add the chocolate and stir to melt.
15Pour through a strainer and keep warm.
17Cut a thin slice from the top of each cake to create a flat surface.
18Place a cake flat-side down on top of each custard. Cover the tops with warm chocolate glaze.