• Preheat oven to 350°F. Line a 17 x 11.5-inch jelly roll pan with parchment paper. Generously sift powdered sugar over a clean, smooth kitchen towel laid flat on your work surface. A thicker tea towel works best. Set aside.
• Separate the egg yolks and egg whites. Place egg whites in a clean metal or glass bowl. Beat on medium-low speed until frothy (about 1½ minutes). Add cream of tartar and continue beating. Slowly sprinkle about ⅓ cup of the sugar into the egg whites while beating. Increase speed and whip until stiff peaks form (about 6–7 minutes).
• In a separate bowl, beat the egg yolks and vanilla with the remaining sugar for 5–6 minutes, until pale, thick, and the mixture forms ribbons.
• Sift ⅓ of the flour iand cornstarch nto the yolk mixture and gently fold. Fold in ⅓ of the whipped egg whites. Repeat, alternating flour and egg whites, until fully incorporated.
• Transfer the batter to the pan and spread it evenly with a spatula. Bake for 12–14 minutes, or until the top springs back when lightly pressed.
• Traditional Cooling Instructions: Cool the cake in the pan on a wire rack for 10 minutes. Run a small knife around the edges, then carefully turn the cake out onto the sugared towel. Peel off the parchment. Starting at the short end, roll the cake up in the towel, snug but not tight. Cool completely on a wire rack.
  
• Preferred Cooling Instructions: As soon as the sponge comes out of the oven, cover the pan tightly with foil to trap steam and keep it soft and flexible. Let it cool at room temperature for 1 hour (do not refrigerate or cool in a cold room, or it may crack when rolled).
  

Strawberry Cream Cheese Filling

• Purée the strawberries until smooth. Strain into a small pan. Add the granulated sugar and bring to a low boil, whisking constantly until reduced to ¼ cup, about 5 minutes. Set aside to cool.
• Add the softened butter and powdered sugar to a mixing bowl. Using a hand mixer or a stand mixer fitted with a paddle attachment, beat on high until smooth. Add the COLD cream cheese and mix until white and fluffy, about 1–2 minutes. Scrape down the bowl as needed. Add the strawberry purée and mix on low speed until just fully incorporated. Chill for 15 minutes.

Assembly

• Traditional Assembly: Gently unroll the cake; it will not completely hold its shape but should remain curved. Add the strawberry cream filling evenly over the cake, leaving about ½ inch uncovered at the end that will be the center of the roll. Re-roll the cake without the towel. Trim the ends and dust with powdered sugar before serving, or pipe on extra cream cheese frosting.
• Preferred Assembly: Spread the strawberry cream filling evenly over the cake, leaving about ½ inch uncovered at the end that will be the center of the roll. Roll the cake by lifting the baking paper with one hand while gently guiding the sponge into a tight roll with the other, keeping even pressure without squashing the filling. Place seam-side down on a serving plate and chill for 1 hour. Trim the ends and dust with powdered sugar before serving, or pipe on extra cream cheese frosting.