Chillingsworth's Lemon Roulade

PreparationMake filling: Whisk together yolks, zest, lemon juice, sugar, and cream of tartar in a 1-quart heavy saucepan. Add butter and cook over moderately low heat, whisking constantly, until curd is thick enough to hold marks of whisk and first bubbles appear on surface, about10 minutes. Immediately pour into a bowl, then chill, covered, until cold, about 5 hours. Make cake: Preheat oven to 400°F. Butter a 15- by 10- by 1-inch shallow baking pan (jelly-roll pan), then line bottom lengthwise with a large sheet of wax paper, letting paper hang over ends by 2 inches, and butter paper. Beat egg whites in a large bowl with an electric mixer until frothy. Add granulated sugar, 1 tablespoon at a time, beating constantly, and beat until whites just hold stiff peaks. Beat yolks in another large bowl with cleaned beaters until slightly thickened and pale, about 5 minutes with a standing mixer or 7 with a handheld. Fold one fourth of whites into yolks to lighten. Pour yolk mixture over remaining whites, then sift flour and cornstarch on top and fold in gently but thoroughly. Fold in vanilla and zest. Spread batter evenly in baking pan and bake in middle of oven until cake is puffed and springy to the touch and top is lightly browned, about 10 minutes. Loosen paper from sides of pan. Sprinkle cake with 1/3 cup confectioners sugar, then cover with another sheet of wax paper and a baking sheet. Invert cake onto sheet and remove baking pan. Cool cake completely and peel paper from top. Assemble roll: Spread filling evenly over cake, leaving a 1/4-inch border on all sides. Put a long platter next to a long side of cake. Beginning with a long side and using wax paper as an aid, roll up cake jelly roll–style. Carefully transfer cake, seam side down, to platter, using wax paper to help slide cake. Chill, covered with plastic wrap, at least 2 hours. Dust cake generously with confectioners' sugar. Slice cake cold, then bring to room temperature before serving. Cooks' notes:• A long serrated knife will cut neat slices without compressing or tearing cake. • Filling can be chilled up to 3 days. • Assembled cake improves in flavor if made 1 day ahead and kept chilled.

PreparationMake filling: Whisk together yolks, zest, lemon juice, sugar, and cream of tartar in a 1-quart heavy saucepan. Add butter and cook over moderately low heat, whisking constantly, until curd is thick enough to hold marks of whisk and first bubbles appear on surface, about10 minutes. Immediately pour into a bowl, then chill, covered, until cold, about 5 hours. Make cake: Preheat oven to 400°F. Butter a 15- by 10- by 1-inch shallow baking pan (jelly-roll pan), then line bottom lengthwise with a large sheet of wax paper, letting paper hang over ends by 2 inches, and butter paper. Beat egg whites in a large bowl with an electric mixer until frothy. Add granulated sugar, 1 tablespoon at a time, beating constantly, and beat until whites just hold stiff peaks. Beat yolks in another large bowl with cleaned beaters until slightly thickened and pale, about 5 minutes with a standing mixer or 7 with a handheld. Fold one fourth of whites into yolks to lighten. Pour yolk mixture over remaining whites, then sift flour and cornstarch on top and fold in gently but thoroughly. Fold in vanilla and zest. Spread batter evenly in baking pan and bake in middle of oven until cake is puffed and springy to the touch and top is lightly browned, about 10 minutes. Loosen paper from sides of pan. Sprinkle cake with 1/3 cup confectioners sugar, then cover with another sheet of wax paper and a baking sheet. Invert cake onto sheet and remove baking pan. Cool cake completely and peel paper from top. Assemble roll: Spread filling evenly over cake, leaving a 1/4-inch border on all sides. Put a long platter next to a long side of cake. Beginning with a long side and using wax paper as an aid, roll up cake jelly roll–style. Carefully transfer cake, seam side down, to platter, using wax paper to help slide cake. Chill, covered with plastic wrap, at least 2 hours. Dust cake generously with confectioners' sugar. Slice cake cold, then bring to room temperature before serving. Cooks' notes:• A long serrated knife will cut neat slices without compressing or tearing cake. • Filling can be chilled up to 3 days. • Assembled cake improves in flavor if made 1 day ahead and kept chilled.