Our friends at America's Test Kitchen call the Boston area home. Assuming they would know a thing or two about it, we wanted to get their thoughts on - and a recipe for - a classic American dessert, the Boston cream pie. Managing Producer Sally Swift also had a few questions for America's Test Kitchen host Bridget Lancaster, who stood firm in defending the honor of Boston's namesake dessert. Try their recipe for Wicked Good Boston Cream Pie.
Sally Swift: I don’t want you to feel responsible for defending Boston cream pie, but I do have two questionas for you. First of all, it’s a cake - so why do we call it a pie? And second, I don’t think I’ve ever had a good piece of Boston cream pie.
Bridget Lancaster: Oh boy. Well.
SS: So, I guess I am asking you to defend it.
BL: [Laughs] You can have good Boston cream pie. I’m like you; it’s hard to find it out in bakeries that are good. Sometimes the cake is rubbery or too sweet. There’s so much sugar, between the sponge cake itself and the custard filling, then the chocolate on top.
The pie part of it that you mention is interesting. We did a lot of research trying to find out exactly what they meant by “pie.” We think – and food historians have told us – that the pie plate was one of the most used pieces of bakery back then. They baked everything in pie plates instead of cake pans. So, it was just natural to call it a pie. At least that’s my story, and I’m sticking with it.
SS: America’s Test Kitchen has taken apart and reassembled this old American recipe for the home cook. Can you tell me what you did?
BL: There are three components to a Boston cream pie. There are two layers of sponge cake, and in between is a layer of vanilla pastry cream. Then they pour chocolate glaze over it.
SS: That should be delicious. And as I’ve said, it has not always been. What did you guys do to make it friendly for home cooks?
BL: We ditched the sponge cake.
SS: You did?
BL: Yes. Traditional sponge is super finicky. You take eggs – either whole eggs or egg yolks – and beat them with sugar until they’re foamy. Then you had to delicately fold in a flour mixture. The little trapped air bubbles from beating the eggs and the sugar together, that’s the only leavening that the cake gets. If you over-fold in the flour, you’re going to deflate the mixture and have a squat Boston cream pie. It’s very rubbery at that point.
We switched over to something called a hot milk sponge cake, which is a little bit of a Betty Draper-style retro recipe. It couldn’t be easier to make. You take milk and a little bit of butter, and heat them together until the butter melts. Take eggs and sugar, and beat that until it’s nice and fluffy. Then you pour in all the milk mixture into that egg/sugar blend. Stir in flour, a bit of salt, and baking powder. Again, baking powder is going to make this foolproof. The cake is going to rise every single time.
SS: Do you do two of those? Or you do one and cut it in half?
BL: It’s much easier to make two. The other part of this is there’s some butter in the cake that makes it more tender and less sweet. A traditional sponge doesn’t have a lot of fat in it. You need that fat to counter the sweetness.
SS: Okay. We have the cake. Now, what goes on with the cream?
BL: There’s two ways to make a traditional pastry cream. Again, you take eggs or egg yolks, and you mix it with sugar. Then you pour in hot half-and-half, and you have to be really careful. You want it to temper; you want it to start to thicken. But you don’t want it to curdle. You also don’t want to undercook it. Otherwise, it can be too thin. We found there are two ways to do this. The starch you can add is either cornstarch or flour. Flour is going to make the pastry cream work every single time. Cornstarch is 100 percent starch, and that does have the ability to thicken very well. But if you don’t heat the mixture enough, there’s some enzyme in the egg yolk that will actually prevent the cornstarch from thickening enough, so you end up with a mixture that’s too thin. Also, if you mix a cornstarch thickened pastry cream a little too much, it will start to thin itself. You basically break down the structure and cause some of the moisture to weep out. In addition to starch, flour has some fats, lipids, and proteins; they work as binders. You not only have the starch from the flour, but these extra powerful binders that thicken the pastry cream. And it stays thick; it works every single time.
SS: Pastry cream is scary for people. It sounds like you have absolutely eliminated that issue for us.
BL: Here’s a little hint that somebody once taught me. If your pastry cream curdles a little bit, it doesn’t really matter. Pass it through a fine mesh sieve, and nobody will ever know.
SS: Last, but not least – the chocolate glaze.
BL: This is the easy one. A lot of chocolate glazes are made from chocolate and heavy cream. You pour it over the cake, but it can be kind of dull. The original recipe – the Boston cream pie that was made in the Omni Parker House hotel in Boston back in the 1850s – mixed chocolate with a fondant mixture. They boiled water and sugar together until it got to the soft-ball stage. There was a bit of cream in there too. Then they added the chocolate, and it made it brittle – almost like candy. We wanted something that was sliceable, something thick enough to cling to the cake – not just pour down into the serving dish – but also stay supple and be very shiny. The key to that is corn syrup. A little bit of corn syrup gives it that flexibility and shine like a freshly polished pair of black patent shoes.
SS: You have really demystified this one. Is this one of those cakes or pies that is better after a day’s rest?
BL: Absolutely. Actually, the whole cake can be made over a few days. The cake can be made a couple days in advance. The pastry cream can also be made a couple days in advance. If you didn’t want to put together the whole thing in one day, that’s fine. But after you put it together, it needs to refrigerate for at least three hours before you slice into it, because it has to set up. Our recipe says 24 hours in advance, but it can definitely sit there for 48 hours at least. I think cakes that have pastry cream in them – or any kind of dessert that has a custard in it – are much better if you give them at least one day in the fridge.
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