Makes 10 to 12 servings
- Active time: 30 mins
Total time: 2 hr (includes 1 hour cooling time for filling)
In the winter months, there’s nothing like the bewitching, slightly exotic flavor of Key limes or the larger regular limes (a.k.a. Persian) to transport you mentally to some warm tropical spot, preferably an island with an endless beach. This cake, with its tart lime filling offset by billowy drifts of sweet, marshmallow-like frosting, should do the trick.
Key limes are smaller than Persian limes and often come packed in a net bag, but don’t despair if you can’t find them. Persian limes make an excellent substitute (see Cooks' Notes, below, for more details on buying limes). Another helpful hint: Because there’s grated zest in both the cake and the filling, grate all the zest you need first, before you start juicing.
INGREDIENTS:
For Cake:
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2 3/4 cups sifted cake flour (not self-rising; sift before measuring) plus more for pans
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2 1/2 teaspoons baking powder
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1/2 teaspoon salt
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2 sticks (1 cup) unsalted butter, softened, plus more for pans
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1 1/2 cups sugar
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4 large eggs, warmed in shell in a bowl of warm water 5 minutes
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1 tablespoon grated Key lime or lime zest
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1 1/2 teaspoons pure vanilla extract
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1 cup whole milk
For Filling:
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3/4 cup sugar
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1/4 cup cornstarch
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Pinch of salt
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3/4 cup water
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3/4 cup fresh Key lime or lime juice
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2 large eggs
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3 tablespoons unsalted butter, cut into tablespoons
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2 teaspoons grated Key lime or lime zest
For Frosting:
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2 large egg whites
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3/4 cup confectioners’ sugar
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2/3 cup light corn syrup
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2 tablespoons water
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1 teaspoon pure vanilla extract
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1 teaspoon fresh Key lime or lime juice
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1/8 teaspoon salt
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For Cake:
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Heat oven to 350°F. with rack in middle. Butter cake pans, then line bottoms with rounds of parchment. Dust pans with additional flour, knocking out excess. Sift flour, baking powder, and salt together into a bowl.
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Beat together butter and sugar in a large bowl with an electric mixer (or a stand mixer fitted with the paddle attachment) at medium-high speed until pale and fluffy, about 3 minutes. Beat in eggs one at a time, beating well after each addition. Beat in zest and vanilla and continue beating until light and fluffy, 3 to 5 minutes more. At low speed, add flour mixture in 3 batches alternately with milk, beginning and ending with the flour mixture and mixing until batter is just smooth.
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Divide batter between cake pans, spreading it evenly. Bake until a wooden toothpick inserted in the center of each cake comes out clean and cakes begin to pull away from sides of pans, 20 to 25 minutes.
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Cool for 15 minutes in pans on racks. Run a thin knife around sides of pans, invert cake layers onto racks, and cool completely.
For Filling:
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Whisk together sugar, cornstarch, and salt in a heavy 2-quart saucepan, then whisk in 3/4 cup water and juice until smooth.
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Whisk together eggs in a medium heat-proof bowl until well combined.
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Bring juice mixture to a boil over medium heat, stirring with whisk, then reduce heat and continue to cook at a slow boil, stirring with whisk, 1 minute (mixture will be thick). Remove pan from heat.
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Add half of hot juice mixture to eggs in a slow stream, stirring with whisk. Stir egg mixture into juice in pan and cook over medium-low heat, stirring, just until it reaches a simmer. Remove pan from heat and add butter and zest, stirring until butter is melted.
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Cover filling with a buttered round of wax paper or parchment paper and chill until cold, about 1 hour.
Assemble Cake:
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Halve each cake horizontally with a long serrated knife. Put 1 layer on a cake stand or a large plate and spread with one-third of filling (about 2/3 cup).
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Stack remaining cake layers using half of remaining filling between each layer. Spread top and side of cake generously with frosting.
COOKS’ NOTES:
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Limes, whether Key or Persian, can vary tremendously in the amount of juice they hold; some can be quite dry and pulpy inside, while others will release plenty of liquid. That makes it difficult to give you, the cook, an idea of how many limes you’ll need. We think you’ll be safe buying a total of 1 1/2 pounds Key limes or 10 medium Persian limes to make the cake layers, filling, and icing. But don’t be surprised if you have extra. Use them up in a batch of margaritas!
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Cake layers (not split) can be made 1 day ahead and chilled, wrapped individually in plastic, or frozen 1 week. Halve chilled layers while still cold, but defrost frozen layers before attempting to halve them. Filling can be refrigerated, covered, overnight. Stir before using.
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The egg whites in the frosting are not cooked. If this is a concern, you can substitute reconstituted dried egg whites, such as Just Whites. Cake can be assembled and frosted 2 hours ahead if using fresh whites, and 6 hours ahead if using dried whites. Alternatively, cake can be filled but not frosted 1 day ahead. Wrap well in plastic and chill. Let stand at room temperature 1 hour before frosting it.
