When I made it, the cake came out very thin after baking, and I was worried I would have a hard time cutting through it, but it ended up being easier than I thought, and the resulting cake was a good size.
Note that the filling needs to set for a while, so make it at least a few hours in advance.
Bostom Cream Cake
For the Filling:
* 2/3 cup milk
* 1/3 cup granulated sugar
* 3/4 cup heavy cream
* 1/4 cup cornstarch
* 1 large egg yolk (save the white for the cake)
* 2 teaspoons vanilla extract
For the Cake:
* 1/4 cup vegetable shortening (I used butter)
* 3/4 cup white rice flour
* 2 tablespoons sweet rice flour
* 2 tablespoons cornstarch
* 1/4 teaspoon xantham gum
* 1/2 cup granulated sugar
* 1 teaspoon salt
* 1.5 teaspoons baking powder
*1/2 cup milk
* 1 large egg
* 1 egg white (left over from the filling)
* 1 teaspoon vanilla extract
For the Icing:
* 4 ounces (about 100 grams) dark chocolate, coarsely chooped
* 1/2 cup heavy cream
1. Prepare the filling: in a medium saucepan over medium-high heat, combine the milk and sugar. Heat, stirring, until the sugar is dissolved.
2. In a small bowl, vigorously whisk together the heavy cream, cornstarch and egg yolk.
3. Reduce the heat under the milk and sugar to low. While whisking the hot milk, very slowly pour the heavy cream mixture into the saucepan.
4. Increase the heat to medium. Whisk mixture constantly until it thickens, about 2.5 minutes. Remove filling from heat, continue to whisk mixture for an additional minute, then whisk vanilla into slightly cooled filling.
5. Pour filling into a large bowl. Place a piece of plastic wrap directly on the surface of the filling, to prevent it from forming a skin.
6. Refrigerate the filling for at least 4 hours, or overnight.
7. Prepare the cake: Preheat oven to 350 F (180 C). Grease a 9 inch (22 cm) round cake pan.
8. In a medium bowl, mix all ingredients for 2 minutes; batter will be thick (if you are using a stand mixture, set it on medium high).
9. Pour batter into pan and bake for 25 minutes or until a tester inserted into the center of the cake comes out clean.
10 remove cake from oven and allow to cool completely (you can take it out of the pan for faster cooling after about 5 minutes).
11. Prepare the icing: Place chopped chocolate into a large bowl.
12. In saucepan or microwave-safe bowl, bring cream to a boil and remove from heat.
13. Pour boiled cream over the chocolate. Stir, using a wooden spoon, until the chocolate melts and no lumps remain. Allow the icing to cool for 8 minutes.
14. Assemble the cake: Using a serrated knife, slice the cooled cake in half horizontally. Gently remove the top portion and set aside.
15. Spread all of the filling onto the bottom half of the cake. Top with reserved cake layer.
16. Ladle lightly cooled icing onto the cake. Refrigerate until ready to serve.