Preheat oven to 350°F (175°C). Line a 10x15-inch jelly roll pan with parchment paper.
Sift cake flour and matcha powder three times to remove lumps.
Whisk egg yolks with 20g sugar until pale and thick. Add milk, oil, and salt.
Fold in sifted dry ingredients gently.
In another bowl, beat egg whites with cream of tartar until foamy. Gradually add 40g sugar until stiff peaks form.
Gently fold meringue into matcha batter in three additions.
Pour batter into prepared pan and spread evenly. Tap to remove air bubbles.
Bake 12–14 minutes, until top springs back when touched.
Flip hot cake onto a sugared towel, peel parchment, and roll up while warm. Cool for 30 minutes.
Whip cream, sugar, vanilla, and mascarpone (if using) until stiff peaks.
Unroll cooled cake, spread cream evenly, then re-roll tightly.
Wrap in plastic wrap, chill seam-side down for 2 hours before slicing.