For the Sponge Cake Layers
Adjust an oven rack to the lower-middle position and heat the oven to 350 degrees. Grease two 8 or 9 inch cake pans and cover the pan bottom with rounds of parchment paper or waxed paper. Whisk the flours, baking powder, and salt in a medium bowl (or sift onto wax paper). Heat the milk and butter in a small saucepan over low heat until the butter melts. Remove from the heat and add the vanilla; cover and keep warm.

Separate 3 of the eggs, placing the whites in the bowl of a standing mixer, reserving the 3 yolks plus the remaining 2 while eggs in another mixing bowl. Beat the 3 whites at low speed until foamy. Increase the mixer speed to medium and gradually add 6 tbs of the sugar; continue to beat the whites to soft, moist peaks. (Do not overbeat.) Transfer the egg whites to a large bowl and add the whole-egg mixture to the mixer bowl.

Beat the while-egg mixture with the remaining 6 tbs sugar. Beat at medium-high speed until the eggs are very thick and a pale yellow color, about 5 minute. Add the beaten eggs tot he whites.

Sprinkle the flour mixture over the beaten egg and whites; fold very gently 12 times with a large rubber spatula. Make a well in one side of the batter and pour the milk mixture into the bowl.Continue folding until the batter shows no trace of flour and the whites and whole eggs are evenly mixed, about 8 additional strokes.

Immediately pour the batter into the prepared cake pans; bake until the cake tops are light brown and feel firm and spring back when touched, about 16 minutes for 9-inch cake pans and 20 minutes for 8-inch cake pans.

Immediately run a knife around the pan perimeters to loosen the cakes. Place on pan on a towel and cover the pan with a large plate. using the towel to protect your hands and catch the cake, invert the pan and remove the pan from the cake. Peel off the parchment. Re-invert the cake from the plate onto the rack. Repeat with the remaining cake. Cool the cake layers to room temperature before proceeding with Boston Cream Pie.

For the Cheesecake Layer
Preheat oven to 325 degrees. Set a kettle of water to boil. Using an electric mixer, beat cream cheese on medium until fluffy, scraping down side of bowl. Gradually add sugar, beating until fluffy. Beat in lemon zest and juice, and salt. Beat in eggs, one at a time, scraping down side of bowl after each addition. Beat in sour cream.

Cut parchment paper in a circle and line the bottom of the cheesecake pan. Wrap bottom half of pan in foil. Pour in filling; place in a roasting pan. Pour in boiling water to come halfway up side of springform. Bake until just set in center, about 45 minutes. Remove pan from water; let cool 20 minutes. Run a paring knife around edge; let cool completely. Cover; chill overnight, then wrap in plastic wrap and freeze.

For the Glaze
Bring the cream and corn syrup to a full simmer over medium heat in a medium saucepan. Remove from the heat and add the chocolate; cover and let stand for 8 minutes. (If the chocolate has no completely melted, return the saucepan to low heat; stir constantly until melted.) Add the vanilla; stir very gently until the mixture is smooth. Cool until tepid so that a spoonful drizzled back into the pan mounds slightly. (The glaze can be refrigerated to speed up the cooling process, stirring every few minutes to ensure even cooling.)

To Assemble the Cake
Place one of the sponge cake layers on a serving plate. Stack the cheesecake layer on top of the sponge cake. Add the second sponge cake layer.

Pour glaze over entire cake and spread to nearly the edge allowing some of the glaze to spill over the side of the cake.