To make the meringue, preheat the oven to 210°F (100°C). Use a stainless steel circle or a plate 7 inches (18 cm) in diameter as a template, and draw two discs on two sheets of parchment paper. Turn them over and place them on two baking sheets.

In a large bowl, place egg whites with a good pinch of salt. Beat with an electric mixer at medium-high speed for 3-4 minutes. Switch the mixer speed to high, and gradually add caster sugar, about 2 tablespoons at a time. Whisk until sugar dissolves and stiff peaks form. Add the sifted powdered (icing) sugar and gently mix with a rubber spatula.

Place the meringue in a pastry bag with the cut end or Ateco plain pastry tip 809. Draw two spiral meringue disks on the parchment paper starting from the center of the circles. Alternatively, divide the meringue evenly between two 7-inch (18 cm) circles drawn on the prepared baking sheets. Use a spatula to spread it out. Bake the meringue layers for about 2 hours. Let them cool completely.

To make mascarpone whipped cream, place cold heavy cream, cold mascarpone, icing (powdered) sugar, and powdered instant coffee in the chilled bowl of a stand mixer with a whisk attachment. Whisk the cream until stiff peaks. Transfer the cream to a piping bag with the end cut about 1/2 inch (1 cm) or fitted with Ateco tip 809.

To make chocolate shavings, use a vegetable peeler, scraping across a chocolate bar, to get medium-sized delicate curls. Make large chocolate shavings by scraping the chocolate with a knife if desired. 

To assemble the cake, place the first meringue layer on a cake board or a serving plate and pipe the mascarpone whipped cream in a spiral. Place the second meringue disk top-down, and spread a thin layer of the cream. Smooth the surface evenly with a bent spatula, mask, and smooth the sides of the cake. Push the cream, making balls over the entire surface of the cake.