Step 1: Preheat your oven to 340°F (170°C) and line a 10×15 inch jelly roll pan with parchment paper.
Step 2: In a medium bowl, whisk the egg yolks with 20g of granulated sugar until pale and frothy.
Step 3: Add the vegetable oil and milk to the yolk mixture, whisking until well combined.
Step 4: Sift the cake flour and matcha powder into the yolk mixture and whisk until the batter is smooth with no lumps.
Step 5: In a separate clean bowl, beat the egg whites with cream of tartar. Gradually add the remaining 50g of sugar while beating until stiff, glossy peaks form.
Step 6: Gently fold one-third of the meringue into the matcha batter to lighten it. Then, fold in the remaining meringue in two batches using a spatula until just combined.
Step 7: Pour the batter into the prepared pan, smooth the top, and tap the pan on the counter to release large air bubbles. Bake for 12-14 minutes.
Step 8: Immediately remove the cake from the oven. Flip it onto a clean kitchen towel dusted with powdered sugar. Remove the parchment paper and roll the cake tightly with the towel from the short end. Let cool completely.
Step 9: Whip the heavy cream and powdered sugar until stiff peaks form. Carefully unroll the cooled cake, spread the cream evenly, and roll it back up. Refrigerate for at least 2 hours before slicing.