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1
Preheat oven to 350u00b0. Lightly coat a jelly-roll pan with baking spray. Line bottom of pan with wax paper. Coat paper with baking spray. Set aside.
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2
To prepare cake, weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, cocoa, baking powder, and salt in a bowl; stir with a whisk. Place egg yolks, 1/4 cup granulated sugar, and vanilla in a large bowl; beat with a mixer at medium speed until light and fluffy (about 4 minutes). Place egg whites and cream of tartar in a medium bowl; beat at medium speed until foamy using clean, dry beaters. Beat mixture at high speed until soft peaks form. Gradually add 1/2 cup granulated sugar, 1 tablespoon at a time, beating until stiff peaks form (do not overbeat). Stir one-fourth of egg white mixture into egg yolk mixture; gently fold in remaining egg white mixture. Sift half of flour mixture over top of egg mixture; gently fold in. Sift remaining flour mixture over top of egg mixture; gently fold in. Spread mixture evenly into prepared pan.
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3
Bake at 350u00b0 for 9 minutes or until cake springs back when lightly touched in the center. Loosen cake from sides of pan; turn out onto a dish towel dusted with 2 tablespoons powdered sugar. Carefully peel off wax paper; cool 1 minute. Starting at short side, roll up the cake and towel together. Place, seam side down, on a wire rack; cool completely (about 1 hour).
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4
To prepare filling, place 1/3 cup granulated sugar, rind, juice, 2 tablespoons butter, and salt in a small saucepan over medium heat. Cook until butter melts and sugar dissolves, stirring frequently (about 4 minutes). Place remaining 1/3 cup granulated sugar, cornstarch, egg yolks, and eggs in a bowl; stir well with a whisk until smooth. Drizzle hot juice mixture into egg mixture, stirring constantly with a whisk. Return mixture to pan. Cook over medium heat until mixture thickens and reaches 180u00b0 on a candy thermometer (do not boil). Pour mixture through a sieve into a small bowl, pressing on solids. Discard solids. Add remaining 1 tablespoon butter, stirring until butter melts and is combined. Cover surface of mixture with plastic wrap. Chill completely.
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5
To assemble roulade, gently stir whipped topping into chilled lemon filling. Unroll cake carefully; remove towel. Spread lemon filling over cake, leaving a 1-inch border around outside edges. Reroll cake; place, seam side down, on a platter. Cover and chill 1 hour. Sprinkle cake with 1 tablespoon powdered sugar. Cut cake into slices.
