How to Make It
Preheat oven to 375°F. Line a 15- x 10-inch jelly roll pan with parchment paper; lightly grease parchment. Set aside.
Beat granulated sugar and egg yolks with a heavy-duty electric stand mixer on medium-high speed until thick and pale, about 4 minutes. Stir in poppy seeds, vanilla, 1 tablespoon of the lemon zest, and 1 teaspoon of the lemon juice.
Beat egg whites in a separate bowl on medium-high speed until soft peaks form, 1 to 2 minutes. Stir one-fourth of the egg whites into granulated sugar mixture. Gently fold in remaining egg whites. Sift cake flour, baking powder, and 1/4 teaspoon of the salt over egg mixture; gently fold just until incorporated. Spread mixture in prepared pan. Bake in preheated oven until cake springs back when touched, about 8 minutes. Cool in pan on a wire rack 5 minutes.
Sprinkle 3 tablespoons of the powdered sugar evenly over cake. Run a knife along the sides of cake; invert onto a parchment paper-lined work surface. Peel off top layer of parchment from cake; discard parchment. Sprinkle 3 tablespoons of the powdered sugar evenly over cake. Starting at 1 short side, carefully roll cake and bottom layer of parchment together. Transfer to a wire rack, seam side down, and cool completely, about 30 minutes.
Beat cream cheese and butter on medium speed until light and smooth, about 4 minutes. Gradually add 1 1/2 cups of the powdered sugar and remaining 1 tablespoon each lemon zest and lemon juice, and 1/8 teaspoon salt; beat until smooth, about 2 minutes. Beat heavy cream in a separate bowl on medium-high speed until medium peaks form, 1 to 2 minutes; fold into cream cheese mixture.
Carefully unroll cake. Spread cream cheese mixture over the cake, leaving a 1/2-inch border. Starting at 1 short side, reroll cake without parchment. Place cake, seam side down, on a serving platter. Cover and chill 2 hours.
Sprinkle cake with remaining 2 tablespoons powdered sugar; garnish with lemon zest.