Preheat oven to 180 °C (350°F). Grease 38x26 cm (15x10 inch) baking pan with butter, then line it with baking paper so the cake seamlessly releases. Grease the baking paper too.

Sift the flour, cornstarch, baking powder, and salt into a large bowl.

Using a hand mixer or a stand mixer beat the egg whites with half of the sugar and pinch of salt on high speed for 5 minutes or until stiff peaks form. Set aside.

In another bowl, beat the egg yolks, sugar, vanilla extract, and lemon zest until pale, about 2 minutes. Add in oil and beat 30 seconds. Add in half of the dry ingredients and mix until incorporated. Using a rubber spatula gently fold in beaten egg whites until half-incorporated, then gently fold in rest of dry ingredients until fully combined and there are no visible streaks of flour or egg whites. Avoid over-mixing.

Spread batter evenly into prepared pan. Bake for 10 minutes or until the top of cake springs back when touched.

Place a kitchen towel on a flat surface and cover it with a piece of baking paper dusted with powdered sugar. Gently turn baked cake onto a prepared kitchen towel, peel of the top layer of baking paper. Slowly roll the cake with a kitchen towel, rolling from the short end to the other short end. Let the cake cool completely.

Add the heavy cream, powdered sugar, and vanilla extract to a large mixer bowl and whip on high speed until soft peaks form, add the mascarpone, lemon juice, and lemon zest to the whipped cream and whip until stiff peaks form. It will happen fairly quickly.

Gently unroll the cooled cake, and spread the filling into an even layer onto the top (you may not spend all the filling, I have had a few tablespoons left). Then carefully re-roll the cake, without the towel this time.

Pour the glaze over the cake or simply dust with powdered sugar. Refrigerate for at least 30-60 minutes before slicing and serving.

In a small bowl, whisk together powdered sugar, milk and lemon juice until smooth. Add more milk if you want it thinner, or more powdered sugar if you want it thicker.