Combine the half-and-half with the vanilla bean seeds in a medium saucepan over medium-high heat. Heat until the mixture it just begins to simmer. Don't let it boil.

While it's heating, whisk together the yolks, sugar, and salt in a medium bowl until smooth. Add the flour to the yolk mixture and whisk until blended.

Remove the half-and-half mixture from the heat and slowly drizzle about ½ cup of it into the yolks, whisking constantly. Slowly pour the tempered egg mixture back into the pan with the rest of the half-and-half, whisking constantly.

Return the saucepan to medium heat and cook, whisking constantly, until the custard thickens slightly, about 1 minute. Reduce heat to medium-low and continue to simmer, whisking constantly, 4-5 minutes.

Increase the heat to medium and cook, whisking vigorously, until bubbles burst on surface, 1 to 2 minutes.

Remove the saucepan from the heat, and whisk in the butter until melted and blended. Press the pastry cream through a strainer set over a medium bowl. Press plastic wrap directly on the surface of the custard and refrigerate until set. This will probably take several hours.

Preheat oven to 325 degrees. Lightly grease two 9-inch round cake pans and line the bottoms with circles of parchment.

Whisk the flour, baking powder and salt together in a medium bowl. Heat the milk and butter in a small saucepan over low heat until the butter is melted. Remove from the heat, add the vanilla, and cover to keep warm.

In a stand mixer with the whisk attachment, whip the eggs and sugar on high speed until light. Remove the mixer bowl from stand. Add the hot milk mixture and whisk by hand until blended. Add the dry ingredients and whisk until blended.

Immediately divide the batter evenly between the two prepared pans. Bake until the tops of the cakes are light brown and a toothpick inserted in the center comes out clean, 20 to 22 minutes.

Transfer the cakes to a wire rack to cool completely in the pans.

Run a small plastic knife around the edge of the pans, and invert cakes onto the wire rack. Peel off the parchment and re-invert the cakes.

To assemble the Boston Cream Pie, place one cake on a serving plate. Whisk the pastry cream briefly to soften, then spoon it onto the center of the cake. With an offset spatula, spread the custard evenly to the edges of the cake. Put the second layer of cake on top of the custard, bottom side up, making sure the layers line up properly. Press lightly on the top of the cake to level it. Refrigerate until the ganache is ready.

In a small saucepan, blend the cream and corn syrup together and bring to a simmer over medium heat. Remove from heat and add chocolate. Whisk gently until smooth. Transfer to small bowl and let stand, whisking occasionally, until it's thickened enough to hold a very soft "piled up" shape. If it's not thick enough to do that, the ganache will run too far down the sides of the cake instead of stopping, tantalizingly, part of the way down.

Pour the ganache onto the center of the cake. With an offset spatula, spread it to the edge of cake, pushing just enough over the sides to form overflow in a few places.

Chill the finished the cake at least a few hours before slicing. The cake may be made as long as 24 hours before serving.