Weigh out all the ingredients; use 6 eggs if yours are small.
Simmer the milk with the tea powder over low heat until it colors like milk tea, cover, and steep 5 minutes.
Combine the warm tea milk with the oil, cake flour, and egg yolks in a bowl.
Whip the egg whites, adding the sugar and lemon juice.
Whip on low speed until the meringue forms fine, glossy, firm peaks.
Whisk the yolk batter until smooth.
Whisk until the batter is silky with no lumps.
Fold one-third of the meringue into the yolk batter to lighten it.
Fold the lightened batter into the remaining meringue until just combined.
The batter should fall in a long thick ribbon that folds back on itself.
Pour the batter into the parchment-lined sheet pan.
Level the batter and tap the pan to release large bubbles.
Bake on the middle-lower rack at 150°C top / 130°C bottom (300°F / 265°F) for about 30 minutes, adjusting to your oven.
When the top is nicely colored, remove the cake and tap the pan to release the steam.
Turn the cake out onto a rack and cool completely.
Whip the cream with the sugar to stiff peaks.
Spoon the cream into a piping bag.
Flip the cooled cake and peel off the parchment to reveal the towel texture.
Pipe a thick line of cream one-third of the way across, and spread a thin layer over the rest.
Roll with the five-step method and press the roll inward at the end.
Refrigerate the rolled cake to set its shape.
If you have no rolling frame, set the cake in a box and chill about 30 minutes.
Slice the chilled cake cleanly.
Wrap the slices in parchment and store in a box.
Admire the perfect tea-scented spiral.
Serve and enjoy every bite.