Baked Sunday Mornings: Boston Cream Pie Cake

This week's assignment for Baked Sunday Mornings is the "Boston Cream Pie Cake" -- a recipe with a name that is simultaneously both redundant (since a "Boston cream pie" is by definition a cake) and clarifying (since the "pie" part of the title might otherwise be misleading to someone who doesn't know that a Boston cream pie isn't actually a pie). The "Boston cream" formulation of a cake or doughnut with cream filling and chocolate frosting is so iconic that once when I was at a doughnut shop in Guadalajara, Mexico, I made a point of trying to describe -- in Spanish -- to the man behind the counter that I wanted the doughnut with cream filling and chocolate frosting, and he looked at me in confusion and said -- in English -- "Boston cream?"

The Baked boys have put a small twist on this classic, by adding some chocolate filling to the traditional vanilla filling. The recipe is intended to make a four layer cake, filled with alternating layers of chocolate and vanilla pastry cream filling, and topped with chocolate glaze. The cake is a hot milk sponge, made by whipping together eggs, sugar, and vanilla, folding in sifted dry ingredients (cake flour, baking powder, salt), and then incorporating a mixture of milk and butter that have been heated until the butter melts.

You divide the batter into two 8-inch cake pans and bake. Whenever I make layer cakes, I always weigh the pans before baking to make sure that I have divided the batter equally between the pans. So I know that I had precisely the same amount of batter in my two pans (well, plus or minus 5 grams, since my scale only measures in 5-gram increments). I must not have done a good job mixing the batter, because one of my cakes rose about 50% higher than the other one. Also, on the bottom of the short cake, there was a small milky layer (probably about 3mm) that looked like it didn't have enough flour incorporated into it, and I had to trim it off. You are supposed to divide each cake in half to create four layers for the final cake. I ended up splitting my tall cake into two layers, and trimming my short cake to match the height of the other two split layers -- so I only ended up only with a three-layer cake instead of four layers.

You have to make the vanilla and chocolate pastry creams in advance of making the cake, since they need to be refrigerated for at least four hours before using them. You make the vanilla pastry cream from egg yolks, sugar, salt, cornstarch, butter, and vanilla (you are supposed to add rum as well, but I skipped it). To make the chocolate pastry cream, you just mix melted dark chocolate into a portion of the vanilla cream. My pastry cream was very thick and set up quite firm almost immediately. After refrigerating it overnight, it kept the shape of the bowl it was in, and I had to whisk it pretty vigorously to get it to a spreading consistency. I'm not sure if adding the rum might have helped maintain a creamier texture, but at least the cream was so thick that I didn't have to worry about the it leaking out of the sides of the cake.

The chocolate glaze for the top of the cake is made from dark chocolate, cocoa powder, corn syrup, sugar, cream, salt, vanilla, and butter. My glaze set up quite nicely, such that it kept the shape of the design I swirled into the top. You are supposed to spread the glaze to the edges of the cake so that it drips down the sides, but mine was so thick that it was hard to get it to go down the sides. In retrospect, I wish I had just covered the top and forgotten about the sides.

By the time I finally got around to assembling the cake, I wasn't feeling particularly optimistic about it -- after all, I had clearly done something wrong mixing the sponge cake batter, and I was missing a whole layer. However, I was pleasantly surprised that this cake was pretty darn tasty. While the sponge cake was moist and had a nice tight crumb, it didn't have much flavor. Nonetheless, when eaten with the vanilla and chocolate pastry creams and chocolate glaze, the cake overall was delicious and very favorably received. The one thing I would change is to use a sweeter chocolate for the glaze. I used Ghiradelli 72% for both the pastry cream and glaze (the recipe specifies 60%-72%), and I thought that the glaze was a bit on the bitter side.

I would like to try making this cake again to see if I could actually get four cake layers and smoother pastry cream. But I was happy with my cake, even with all of its imperfections!

Recipe: "Boston Cream Pie Cake," from Baked Explorations: Classic American Desserts Reinvented, by Matt Lewis and Renato Poliafito, recipe available here at Baked Sunday Mornings.


Kris' Kitchen said…
I think our cakes are as close to exactly the same as possible...only I got mad a mine and slopped it together just to get done. It tastes good, but....not what I was after.
Jaime said…
WOW! You got some serious lift on those sponge cakes. I too only got three layers (and that yucky rubbery film on the bottom), but mine weren't nearly as high as yours. Well done. I think I am going try this again too... I have a few ideas on how to improve it as well. Well done!
Sheri said…
I did the same thing - weighed my batter, and I still had one that rose more than the other.

My finished product looks like the Leaning Tower of Pisa.
mike509 said…
That's one beautiful cake - those layers are so high! Nicely done - it looks just like they describe it - gooey and decadent.
Bourbonnatrix said…
wow! your cake looks great! good job!
Elaine said…
Your cake looks wonderful! Thank you for the tip about weighing your cake pans to make sure you have even amounts. I just eye ball it and invariably get uneven layers. In felt the same way about the ganache that I should have just left it on top, but then it was just so delicious mixed with the pastry creams and sponge cake that you really needed to have extra ganache with each bite. You did a beautiful job!