Stir together milk and cornstarch in a medium bowl until smooth. Whisk in the whole egg and yolks until the mixture is smooth.
In the saucepan, stir together cream, sugar, and vanilla bean and slowly bring to a boil. When it reaches the boiling point with just a few bubbles on the surface, add a ladle of the hot cream mixture to the egg mixture and whisk to temper the eggs. Stir the tempered eggs into the cream mixture. Cook, stirring constantly, until the mixture thickens enough to coat the back of a spoon. Stay with it! Don't be tempted to wander off or try to multi task on this one, because it can bubble up and boil over in a second. Strain the custard to remove the vanilla pod and any lumps, then pour into small bowl. Chill in the refrigerator and keep chilled until read to serve.
Preheat the oven to 325° F.
In the large bowl, add the cake flour, sugar, baking powder, and salt. Add the oil, egg yolks, milk, vanilla seeds, and almond extract. Stir mixture until smooth, but do not over mix it.
In the bowl of the stand mixer, beat the egg whites until frothy. Add the cream of tartar and continue beating on high until soft peaks form. Add the beaten whites to the cake mixture and fold in gently. Pour into the sprayed custard cups.
Bake for about 25 minutes, until the cake bounces back lightly when you press it with your finger. Remove from the oven and allow to cool on a wire rack. Once the cakes are completely cool, then remove them from the cups. Cover with plastic wrap to maintain moisture and set aside until ready to serve.
GLAZE: Melt the unsalted butter in a small saucepan over low heat. Remove from heat and stir in the chopped chocolate until it is fully melted. Strain if necessary and keep warm.
ASSEMBLE: Wait until you are ready to serve dessert before assembling, otherwise the cake will get a little stiff and the chocolate will firm up. Pour the custard into bowl or onto a plate. If necessary, level each cake with a serrated knife. Lay a cake on top of each pool of custard, then drizzle the chocolate glaze over top. Garnish with toasted sliced almonds if desired. Serve immediately.