In a medium saucepan over medium heat, heat half-and-half until just beginning to simmer.
In a medium bowl whisk together the yolks, sugar, and salt until combined. Whisk in the flour until combined and no flour pockets remain. Take the half-and-half off of the heat, and slowly whisk in 1/2 cup of the half-and-half to yolk mixture to temper.
Pour the tempered yolk mixture into the half-and-half in the saucepan. Return the saucepan to medium heat and cook, whisking constantly, until the mixture becomes slightly thickened, about 1 minute.
Lower the heat to medium-low and continue to simmer, whisking constantly, for 8 minutes. Then, increase the heat to medium and cook, whisking vigorously, until bubbles burst on the surface, about 1-2 minutes. Take the saucepan off of the heat and whisk in the butter and vanilla until the butter is melted and incorporated.
Set a fine-mesh strainer over a medium bowl and pour the pastry cream through the strainer. Lightly spray a piece of plastic wrap with nonstick cooking spray and place it directly on the surface of the pastry cream. Chill in the refrigerator for at least 2 hours or up to 24 hours.
MAKE THE YELLOW CAKE:
Move the oven rack to the middle position and preheat the oven to 325 degrees F. Spray two 9-inch round cake pans with nonstick cooking spray and line the bottoms with parchment paper. In a medium bowl whisk together the flour, baking powder, and salt; set aside.
In a small saucepan, heat the milk and butter over low heat until the butter is melted. Then, remove the pan from the heat and stir in the vanilla. Cover to keep warm.
In a stand mixer fitted with a whisk attachment, or using a hand mixer fitted with a whisk attachment, whisk the eggs and sugar together on high speed until light and airy, about 4-5 minutes. Slowly whisk in the hot milk and butter until combined.
Add in the flour mixture and pulse the mixer on and off until the flour is just combined. Quickly divide the batter evenly between the prepared cake pans.
Bake the cakes until a toothpick inserted comes out clean and the tops are light brown, about 20-25 minutes. Move the cake to a wire rack to cool completely in the pans. Invert the cakes onto wire racks and then carefully peel off the parchment paper. Then, invert the cake again.
ASSEMBLE THE CAKE:
Put one of the cakes in the center of a cake plate or pedestal. Spoon the pastry cream onto the cake and spread it evenly to the cake edges.
Gently place the second cake round on top of the pastry cream so the cake is bottom side up. Using your fingertips, gently press onto the cake to make it level. Place the cake in the refrigerator while you make the chocolate glaze.
MAKE THE CHOCOLATE GLAZE:
In a small saucepan over medium heat bring the cream and corn syrup to a simmer. Remove the cream mixture from the heat and add the chocolate. Let the mixture sit for 1 minute, and then whisk until combined and smooth, about 30 seconds. Let the mixture sit, whisking every minute until the chocolate has thickened slightly, about 5 minutes in total.
Pour the chocolate glaze onto the center of the cake. Use an offset spatula to spread the glaze to the edges of the cake, letting some of the glaze drip down the sides of the cake. Chill the cake in the refrigerator for at least 3 hours before serving.