According to some Omni Parker House research, the 1855 Boston cream pie had only two layers. The version served now in Parker's Restaurant consists of three layers of spongecake, which are soaked with rum syrup, spread with whipped-cream-lightened custard, topped with chocolate and vanilla icing, and garnished with toasted sliced almonds.
This recipe makes 4 cups of custard filling, a fine amount if you're going to cut the cake into three layers. If you plan to cut the cake into two layers (as below), however, you might prefer to make a half portion of the pastry cream.
For the pastry cream:
1 Tbsp butter
2 cups milk
2 cups light cream
1/2 cup sugar
3-1/2 Tbsp cornstarch
1 tsp dark rum
For the chocolate fondant icing:
2 cups sugar
1/8 tsp cream of tartar
1 cup water
3 ounces semisweet chocolate
1/2 cup sliced almonds
For the cake:
1 cup sugar
1 cup flour
2 Tbsp butter, melted
To make the pastry cream, combine the butter, milk, and light cream in a medium saucepan over medium-high heat. Bring just to a boil.
In a medium bowl, whisk together the sugar and cornstarch. Add the eggs and beat until ribbons form, about 5 minutes. Whisk into the hot-milk mixture and bring to a boil, whisking constantly (to prevent the eggs from scrambling) until the mixture has thickened, about 1 minute. Transfer to a bowl and cover the surface with plastic wrap (to keep a skin from forming). Refrigerate for several hours. Whisk in the rum.
Combine the sugar, cream of tartar, and water in a heavy-bottomed pot over medium heat. Bring the mixture to a boil, stirring to dissolve the sugar. Cover and let boil for 3 minutes. Uncover and dip a pastry brush in cold water to wash down the sides of the pot; boil until the syrup reaches the soft-ball stage (238°F (114°C)), about 5 minutes. Remove from the heat and pour onto the damp cookie sheet. Let it cool for 10 minutes, or until lukewarm.
Using a metal spatula, spread the sugar mixture out and turn it over on itself until it starts to thicken and whiten. (It may be easier to knead the mixture with your hands.) Continue kneading the sugar mixture until it is very stiff. Scrape it off the sheet, place in an airtight container, and refrigerate for several hours.
To make the cake, preheat the oven to 350°F (175°C). Lightly grease a 10-inch springform pan. Separate the eggs, putting the whites in one medium bowl and the yolks in another. Add 1/2 cup of sugar to each bowl. Beat the egg whites until they form stiff peaks; beat the egg yolks until they are thick and pale yellow in color, about 5 minutes. Gently fold the stiff egg white mixture into the yolk mixture. Gradually fold in the flour and then fold in the melted butter. Pour the batter into the prepared cake pan and bake for 18 to 20 minutes, or until a cake tester comes out clean when inserted into the center of the cake. Let cool.
To assemble, heat 3/4 cup of the fondant and the chocolate in a double boiler until warm. Stir to a spreading consistency, adding a little water as necessary.
Using a long serrated knife, slice the cake into 2 layers. Spread the pastry cream over the bottom layer, reserving approximately 1 cup of pastry cream to spread around the sides of the cake (to help the almonds adhere). Place the second layer of cake over the pastry cream and spread the reserved pastry cream around the sides of the cake. Top with the chocolate icing (work rapidly, since the icing sets very quickly) and press the almonds around the sides. Serve immediately at room temperature, or refrigerate for up to 2 days and bring to room temperature before serving. (When refrigerated, the fudge-like icing becomes quite stiff.)
Yield: Serves 10