Preheat the oven to 180º C/ 350º F. Grease very well two 7 inch/ 18 cm cake pans and line them with circles of parchment paper.
Sift together all-purpose flour and cocoa powder. Add baking powder, baking soda and salt and mix well. Set aside.
In a large bowl beat eggs and sugar with an electric mixer for 5-6 minutes or until the mixture doubles its volume. Add oil and vanilla and beat for 1 more minute. Add yogurt and beat again to combine.
Using a rubber spatula fold the dry ingredients into the egg mixture, adding them in 3-4 portions. Mix gently to keep the air inside the batter.
Divide the batter between the prepared pans, adding just a bit more to one pan.
Bake for 40-50 minutes or until a toothpick inserted in the centre of each base comes out clean.
Let the layers cool completely before assembling the cake.
Preheat oven to 110º C/ 200º F.
Using an electric mixer beat egg white and cream of tartar for 1-2 minutes, until foamy. Gradually add sugar, while beating continuously. Beat for few more minutes, until stiff peaks form.
Use a piping bag and a star shaped tip to pipe different size meringues on a baking tin lined with parchment paper.
Bake for 1,5 hours or until the meringues are stuff and hard. Increase the oven temperature to 130 degrees and bake for few more minutes, to get a slightly caramel shade. Watch the meringues carefully to avoid burning them.
Let cool until room temperature before decorating the cake.
In a large mixing bowl using an electric mixer beat mascarpone, cocoa powder and icing sugar: first at a low speed and then at a high speed, until fluffy.
Melt the chocolate on a double boiler. Mix it gently with a rubber spatula to cool it down.
Little by little add from the mascarpone mixture to the chocolate. Mix energetically to avoid the chocolate from hardening quickly. Add more mascarpone and keep mixing, until a smooth creamy texture is created. Fold the chocolate mixture into the remaining mascarpone mixture, until the icing becomes smooth.
Chocolate whipped cream:
In a large mixing bowl beat all the ingredients with an electric mixer, first at a low speed and then at a high speed, until fluffy and smooth.
Using a long serrated knife cut each cake base horizontally into 2 and 3 layers respectively (one of the bases should be slightly taller).
Place one layer on a serving plate and spread about ¼ of the mascarpone icing on top. Place another layer and spread ½ of the whipped cream on top. Continue the process, alternating the two kinds of icing. Make sure you keep a bottom layer for the top of the cake. You can also use a cake ring to make the assembly easier.
After placing the last layer on top, spread the remaining ½ of the mascarpone icing all around the cake using an offset spatula. Leave about 2 tablespoon of the icing to pipe on the cake.
Refrigerate the cake for 4-6 hours before decorating and serving. Make sure you place the meringues on the cake right before serving as they would melt in the fridge.
Decorate and dust lightly with cocoa powder on top.