• Preheat the oven to 340F (170C). Grease and line the bottom and sides of a 8 inch (20 cm) pan with parchment paper.

Prepare vanilla sponge cake.

• Separate whites from yolks.
• In a medium bowl mix yolks with ½ cup (100g) sugar, until creamy and pale yellow colored. Gradually mix in oil and then add sparkling water.
• In a large bowl mix egg whites with salt until foamy. Gradually add remaining ½ cup sugar. Mix in vanilla extract.
• Continue mixing until stiff peaks form.
• Gently fold a spoon of whipped whites into the yolk mixture and then gently fold the yolk mixture into the whipped whites.
• Gradually sift the flour and baking powder over the egg mixture and gently fold them in.
• Pour the batter into the prepared pan.
• Bake for 40-50 minutes, until a toothpick inserted into the center comes out clean.
• Let it cool for about 10-15 minutes. Remove from the pan and cool completely on a rack.

Prepare Mascarpone Frosting.

• In a large bowl mix mascarpone until smooth. Add powdered sugar and vanilla and mix until combined.
• In another bow whip cream until stiff peaks form. Gradually fold into Mascarpone mixture.

Assemble the cake.

• Divide the sponge cake into 4 layers. Place one cake layer on your serving plate.
• In a bowl mix coffee with Marsala if using.
• Brus the cake with coffee mixture. Spread evenly with Mascarpone frosting. Repeat with the second and third layer of cake. Add the last layer of cake, brush with coffee and cover the top and sides with a thin layer of frosting for crumb coating. Refrigerate for 15 minutes.  Cover the top and sides with remaining frosting.
• Decorate the bottom of the cake with chopped chocolate.
• Refrigerate for at least 1 hour before serving.

Meanwhile, prepare white chocolate decoration.

• Melt 2.5 oz (70g) white chocolate over bain-marie. Remove from heat and add remaining chopped white chocolate for tempering. Stir until melted.
• Spread chocolate evenly into a thin layer on parchment paper. Dust with instant coffee powder and refrigerate until slightly set, for about 10-15 minutes. Use round cookie cutters to cut the chocolate. Refrigerate until completely set and ready to use.
• Dust the cake with cocoa powder. Decorate with chocolate disks and pipe remaining Mascarpone frosting if desired. Enjoy.