Boston Cream Pie (6" cake)

Make the pastry cream:

1. Add egg yolks, sugar and salt into a small heat-safe bowl.
2. Whisk in the cornstarch, all-purpose flour and vanilla extract.
3. In a small saucepan, heat up whole milk until scalding hot (don't let it boil).
4. Temper the eggs by gradually pouring the warmed milk in a stream, while constantly whisking, until all the milk is added to the egg mixture.
5. Pour the mixture back into the pot and cook over low heat, until thickened and reaches a temperature of 175F.
6. Remove from heat and strain through a sieve into a clean container.
7. Place a piece of parchment paper over the top of the cream.
8. Cool completely, cover and chill in the fridge until ready to use.

Make the cake:

1. Preheat oven to 325°F/163°C.
2. Line two 6" round cake pans with parchment paper. Set aside.
3. Separate egg whites from egg yolks while cold from the fridge.
4. Add the egg yolks to a large mixing bowl, and whisk in 20g sugar, oil, milk, and vanilla extract.
5. Sift cake flour and baking powder into the egg yolk mixture and mix until just incorporated. Set aside.
6. To a clean stand mixer bowl fitted with a whisk attachment, add in the egg whites and being whisking until bubbles form.
7. Add in cream of tartar and continue whipping until foamy.
8. Gradually pour in remaining 20g sugar and increase the speed, whipping until the meringue reaches soft peaks.
9. Transfer about ⅓rd of the egg white mixture into the egg yolk mixture and fold it in with a spatula.
10. Continue to fold in the egg white meringue mixture into the egg yolk mixture until all of it is incorporated, with no trace of white streaks.
11. Use a kitchen scale to divide the cake batter evenly between the two prepared cake pans.
12. Give the pans a few taps to release any trapped air bubbles.
13. Bake at 325°F/163°C for 15-18 minutes, or until the tops of the cakes spring back when lightly pressed (or a toothpick inserted comes out clean).
14. Remove the cakes from the oven and immediately drop them onto the counter from a height of about 1' to prevent the cake from shrinkage.
15. Use a knife to release the edges of the cake.
16. Transfer cakes to a wire rack to cool completely.

Make the ganache:

1. Add chopped dark chocolate to a heat-proof measuring cup.
2. Pour heavy cream into a microwave-safe bowl or jar.
3. Heat heavy cream in the microwave for 20-30 seconds, or until warm.
4. Pour the warmed cream over the chopped dark chocolate and let it sit for 5 minutes undisturbed.
5. After 5 minutes, stir the mixture until the chocolate is completely melted.

Assemble:

1. Place a layer of cake on a cake board or plate.
2. Use an offset spatula to spread a thick layer of pastry cream over the surface of the cake.
3. Add the second layer of cake over the pastry cream.
4. Pour the chocolate ganache over the top surface of the cake, using an offset spatula to smooth it to the edges.
5. Place the cake into the fridge to set, about 2 hours.