Preheat the oven to 175ºC/350°F/Gas mark 4

Grease two 23cm x 4cm (9-in x 1½-in) cake tins, line the bottoms with parchment paper, then grease again and flour

In a medium-sized mixing bowl, lightly combine the egg whites, ¼ of the milk and vanilla extract

In a large mixing bowl combine all the dry ingredients and mix on low speed for 30 seconds to blend

Add the butter and remaining ¾ of the milk. Mix on a low speed until the dry ingredients are moistened

Increase to medium speed (high speed if using a hand mixer) and beat for 1½ minutes to aerate and develop the cake's structure

Scrape down the sides

Gradually add the egg mixture in 3 batches, beating for 20 seconds after each addition to incorporate the ingredients and strengthen the structure

Scrape down the sides again

Scrape the batter into the prepared pans and smooth the surface with a spatula. The pans should be about half full

Bake for 25-35 minutes or until a skewer inserted near the centre comes away clean and the cake springs back when pressed lightly in the centre. The cakes should start to shrink from the sides of the pans only after removal from the oven

Allow the cakes cool in the pans on wire racks for 10 minutes

Loosen the sides with a small metal spatula and invert onto two other greased wire racks. To prevent splitting, flip over again so that the tops face up. Allow to cool completely before frosting

With an electric mixer on medium speed, whisk the whipping cream until stiff peaks form (be careful not to overbeat, or the cream will become grainy)

In another bowl, whisk together the mascarpone and icing sugar until smooth

Gently fold the whipped cream into mascarpone mixture until completely incorporated

Use immediately to frost the top of one cake

Place the other cake on top of the first and frost the top & sides