Julia Child’s Lemon Poppy Seed Cake

Ingredients

• 6 eggs separated, at room temperature
• 1 cup plus 3 tablespoons granulated sugar
• 3 tablespoons poppy seeds
• 1 tablespoon pure vanilla extract
• 1 cup plus 2 tablespoons plain unbleached cake flour
• 6 tablespoons unsalted butter, melted and cooled
• 6 tablespoons hot water
• 2 tablespoons sugar
• 1 1/2 tablespoons rum
• 6 tablespoons unsalted butter
• 1 2/3 cups sugar
• 2 eggs
• 2 egg yolks
• 2 teaspoons grated lemon zest (from 1 lemon)
• 1/4 cup fresh lemon juice
• 1 tablespoon rum (optional)
• 3/4 cup (6 ounces) unsalted butter, at room temperature
• 3 cups sifted powdered sugar
• 1/3 cup Lemon Curd

Steps

1. Preheat oven to 350°F. Butter 2 (8-inch) round cake pans and line bottoms with rounds of parchment or wax paper. Butter and flour pans, tapping out excess flour.
2. Beat egg yolks in a large bowl. Gradually add 1 cup of the sugar and beat until mixture thickens to the consistency of mayonnaise. Beat in poppy seeds and vanilla.
3. Beat egg whites in a separate large bowl, using clean beaters, on high speed for 6 seconds. Reduce speed to moderately low and continue beating, gradually working your way back up to high speed, until whites form soft peaks. Sprinkle in the remaining 3 tablespoons sugar and beat whites to stiff, shiny peaks.
4. Scoop 1/4 of the whites into yolk mixture and gently fold in. Sift 1/3 of the flour on top of batter and fold in. Repeat 2 more times, to fold in 1/3 of the flour and 1/3 of the egg whites at a time until everything has been incorporated; fold in melted butter with the last of the egg whites.
5. Immediately pour batter into prepared pans. Bang pans once lightly on countertop or work surface to force out any air bubbles. Bake in lower third of the oven until cakes just begin to shrink from the pans, 20 to 25 minutes. Let cakes cool in pans on a rack for 30 minutes. Invert cakes onto rack, peel off paper and let cool completely.
6. Combine sugar, water, and rum in a small pot over low heat and stir until sugar is completely dissolved. Remove pan from heat and let cool.
7. Combine butter, sugar, eggs, egg yolks, lemon zest, lemon juice, and rum in a medium stainless steel saucepan and whisk over very low heat until bubbles begin to subside and a tiny wisp of steam appears; do not boil. Transfer lemon curd to a bowl and place over a bowl of ice until cooled and lightly thickened; whisking occasionally.
8. Beat butter in a medium bowl until softened, then beat in powdered sugar until light and fluffy. Beat in 1/3 cup of the cooled lemon curd until smooth.
9. Using a long serrated knife, slice each cake in half horizontally and place on a work surface, cut side up.
10. Gently brush each cake layer with 2 tablespoons of the rum syrup. Center bottom layer of cake on a platter cut side facing up and spread 1/3 of the lemon curd over it. Place second cake layer on top, cut side facing down, taking care to line up edges. Spread with lemon curd. Repeat with remaining cake and lemon curd, ending with a cake layer.
11. Spread a very thin layer of lemon buttercream over top and sides of cake to keep wandering crumbs in place. Then spread a 1/4-inch layer of buttercream over top and sides.