Fluffy Sponge Cake with Mascarpone Cream Filling

1. Prepare the Sponge Cake:
Preheat oven: Set the oven to 160°C (320°F). Line a 9-inch round or square pan with parchment paper.
Mix wet ingredients: In a bowl, combine the cooking oil, milk, and vanilla extract. Add the egg yolks and whisk until smooth.
Incorporate dry ingredients: Gradually sift the cake flour into the wet mixture, stirring until just combined. Avoid overmixing.
Whip egg whites: In a clean, grease-free bowl, add the egg whites and lemon juice. Whisk until frothy, then slowly add the sugar in 3 additions while beating. Continue whipping until stiff peaks form.
Fold batter: Gently fold one-third of the whipped egg whites into the yolk mixture to lighten it. Then carefully fold in the remaining whites until fully incorporated, ensuring you don’t deflate the batter.
Bake: Pour the batter into the prepared pan, tap gently to remove air bubbles, and bake for 25–30 minutes or until a toothpick inserted in the center comes out clean.
Cool: Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
2. Prepare the Mascarpone Cream Filling:
Whisk mascarpone: In a bowl, combine the mascarpone cheese, sugar, and vanilla extract. Whisk until smooth.
Whip cream: In a separate bowl, whip the heavy cream to stiff peaks.
Combine: Gently fold the whipped cream into the mascarpone mixture until smooth and fluffy.
3. Assemble the Cake:
Slice cake: Once the sponge cake has cooled completely, slice it horizontally into two or three layers, depending on your preference.
Fill layers: Spread an even layer of mascarpone cream between each cake layer.
Decorate: Use the remaining mascarpone cream to frost the top and sides of the cake. Decorate as desired with fruits, nuts, or a dusting of powdered sugar.