Chocolate Semifreddo

Soft Serve

I immediately ruled out using whipped egg whites to lighten the custard, as they tended to produce a chewy, marshmallow-like semifreddo. I wanted a version that was lush and rich, so whipped cream would be my aerator of choice.

I started with a particularly rich custard from my research: I heated ¾ cup of heavy cream in a saucepan, thoroughly whisked it into five beaten egg yolks mixed with a few tablespoons of sugar, and poured the custard back into the saucepan to cook gently until it reached 160 degrees. I then introduced a nifty trick: I quickly poured the hot custard over 8 ounces of chopped bittersweet chocolate so that the chocolate melted, which saved me the extra step of melting it beforehand. Once the custard cooled, I gently folded in softly whipped cream. Finally, I poured the custard into a plastic wrap–lined loaf pan (that way, it would detach more easily from the pan) and froze it until solid, which took about 6 hours.

But I had gone overboard: While the semifreddo had deep chocolate flavor, it was so rich that I couldn't eat more than a few bites. Also, despite the fact that it had just come out of the freezer, it seemed to lack a certain refreshing coldness. I decided to cut some richness from the next batch of custard by replacing the heavy cream with an equal amount of milk. The dessert tasted lighter for sure—too lean, in fact. And in contrast to the fattier semifreddo, this one seemed overly cold, almost like a popsicle. It also melted a lot faster.

I would obviously need to add back some fat, so for my next batch, I used heavy cream cut with ¼ cup of water (this combo still had more fat than milk alone). This time I nailed it: The semifreddo was lush, sliced neatly, and—interestingly—tasted cold without feeling numbingly so. The only drawback was the fussy step of separating all those eggs, so I tried again with a combination of heavy cream, water, and three whole eggs instead of five yolks. The results were even better—the perfect balance of decadent and refreshing, thanks to the extra water in the egg whites—and the method was easier and less wasteful.

But I was curious to learn why the dessert had seemed more or less cold, depending on how much fat was in it. After a conversation with our science editor, I understood: When you put a spoonful of frozen dessert on your tongue and you feel its coldness, that's because heat energy is transferring from your tongue into the dessert, making your tongue colder. The extent to which that happens—and hence the amount of coldness you feel—depends not only on the temperature of the dessert but also on its ingredients, such as the amount of fat versus water.

Try this little experiment: Reach into your freezer, pull out an ice cube and a stick of butter, and grasp them for a minute. They're both the same temperature, but the ice cube feels colder. That's because frozen water can take in more heat from your body (and more quickly) than frozen fat, so your hand loses more heat and feels colder. For the same reason, at equal serving temperatures, an ice cream with more fat in it will seem less cold in your mouth than a leaner recipe.

Science: Keeping Semifreddo in Shape

Fat and air help semifreddo resist melting and keep its shape once it’s out of the freezer. Our semifreddo has an abundance of butterfat, and butterfat melts well above room temperature. Even more important, the air from the whipped cream acts as an insulator, slowing the transfer of ambient heat much like the fluffy feathers in a down jacket. It’s this latter factor that allows our semifreddo to retain its shape longer than most ice creams, since whipped cream contains more trapped air than what’s introduced into ice cream during churning.

To demonstrate how air acts as an insulator, we compared how quickly 1 cup of frozen unwhipped heavy cream would melt versus 1 cup of heavy cream that we whipped before freezing. The frozen unwhipped heavy cream began to slump and soften after about 15 minutes and was ringed by a puddle of liquid after 45 minutes; meanwhile, the frozen whipped cream remained comparatively firm and exhibited little melting.

All Dressed Up

Though some semifreddo recipes call for mixing candied fruit, nuts, or cookies into the custard, I enjoyed my version's smooth, creamy texture and was hesitant to change it. But a garnish would offer textural contrast and make the dessert look more festive.

In my research I'd seen a chocolate semifreddo with a deep red cherry sauce spooned over each slice, so I put together my own version made with frozen sweet cherries, sugar, kirsch (cherry brandy), and a little cornstarch for body. The color and flavor were vivid, and the plump fruit nicely complemented the satiny semifreddo. For a bit of crunch, I made a batch of candied nuts with a pinch of salt to contrast with the dessert's sweetness.

Rich and satiny. Elegant. Deeply chocolaty. Make-ahead (you can even slice off a portion and freeze the rest for later). No ice cream maker required. Time to plan another dinner party.

Keys to Success

• Streamlined, easy-to-follow recipe

  We simplify the process by cooking the custard on the stove and then straining the mixture directly over the chocolate to melt it instead of preparing them separately over a double boiler. We also skip the fussy meringue or whipped egg whites and use simple whipped cream instead.

• Smooth, rich, and creamy but still refreshing

  Using whole eggs and a mix of heavy cream and water ensures that the semifreddo has a balanced amount of fat and water so it's rich and creamy but doesn't soften too quickly and that it tastes cold and refreshing, not icy or too mouth-coating.

• Contrasting texture and elegant garnishes

  Crunchy candied nuts and a sweet cherry sauce add contrast and elevate this simple dessert to company-worthy status.

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