Poppy Seed Cake

To make the cake: Grate the zest from the orange, and soak it, along with the poppy seeds, in the buttermilk for 15 minutes.

Preheat the oven to 350 F. Place the butter in the bowl of a mixer and add the sugars. Start beating on low speed to incorporate, then raise the speed to high and beat, scraping the sides of the bowl occasionally, until the mixture is light and fluffy. Add the egg yolks one at a time, beating well between each addition, then add the vanilla.

Sift the flour with the baking powder and salt and add alternately to the batter with the buttermilk mixture. In another bowl, beat the egg whites until stiff peaks form. Beat one-fourth of the meringue into the batter to lighten it, then gently fold in the remaining whites.

Line a 12-1/2-by-17-1/2-inch jelly roll pan with parchment paper. Butter and flour the paper. Gently spread the batter evenly in the pan and sprinkle the top with the cinnamon. Bake in the preheated oven for 25 to 30 minutes, or until the top is lightly browned and springs back when touched. Remove from the oven and cool on a rack.

To make the buttercream: Combine the sugar and water in a heavy saucepan and bring to a boil over high heat. Cook to the small-crack stage (290 F). While the sugar syrup is cooking, beat the egg yolks at high speed in a mixer bowl until light and lemon colored. With the mixer running, slowly pour the syrup into the yolks. Continue beating until the mixture is cool, about 3 to 5 minutes. Add the softened butter bit by bit and continue beating until the frosting has a shiny look to it. Add the orange zest and set aside.

To make the creme fraiche: Whisk together the heavy cream and sour cream, cover with plastic wrap, and allow to stand at room temperature for 24 hours. Refrigerate at least 12 hours before using.

To assemble: Butter and line a 13-by-4-1/2-inch loaf pan with parchment paper. Using the bottom of the loaf pan as a guide, cut 2 pieces of cake the same size. Slice the layers in half lengthwise to create 4 thin layers.

Place 1 layer of cake at the bottom of the loaf pan, and spread one half of the creme fraiche over it. Top with sliced peaches, and place a second cake layer in the pan. Spread with one half of the buttercream and top with peaches. Repeat with the third and fourth layers, ending with buttercream. Chill the cake 1 hour.

Run a knife along the sides of the loaf pan. Invert the cake onto a serving platter, wrapping the pan in hot towels to facilitate loosening it. Lift the pan off the cake.

Cut 2 pieces of waxed paper into 20-by-3-inch strips. Place the white chocolate in a small deep pan over another pan of simmering water and stir until melted. Sprinkle with 2 tablespoons of poppy seeds, then spread melted white chocolate over the poppy seeds with a spatula. Place the strips on a chilled marble slab, or in the refrigerator on a cookie sheet, and when firm but pliable press the chocolate strips against the long sides of the cake. Trim the ends and use the trimmed pieces for the ends of the cake. Return the cake to the refrigerator and allow the chocolate to chill hard. Then peel off the waxed paper.

Decorate the top of the cake with additional peach slices, and sprinkle with 1 teaspoon of poppy seeds.

Note: This cake can be made up to one day before serving and kept in the refrigerator. Allow it to sit at room temperature for 1 hour before serving.