Preheat oven to 350°F. Line the bottom of the 9-inch springform pan with parchment paper.
In a large microwave safe mixing bowl, melt the chopped chocolate at 0:30 seconds increments to ensure not to scorch chocolate. Once melted, add in butter and stir to combine and melt butter. Set bowl aside.
In another mixing bowl, with a whisk, add ½ cup of sugar to whole eggs. Whisk until combined and frothy. Add in vanilla and salt. Add eggs to chocolate mixture and mix to combine. Set bowl aside.
In a mixing bowl with an electric mixer with whisk attachment, whisk egg whites until quite foamy. Add slowly the ½ cup of sugar to the egg whites. Beat until the peaks are soft and hold the shape but are not stiff. Fold ¼ of the egg whites into the chocolate mixture, and then fold in the rest of the egg whites carefully. Pour the batter into the pan and smooth the top with spatula.
Bake the cake for approximately 35-40 minutes. The top of the cake will be puffed, and the center will not be wobbly. Do not overbake the cake.
Cool the cake in the pan on a wire rack. The cake will fall as it cools and the top will be cracked.
When ready to serve, take the 2 cups of heavy cream out of the refrigerator pour in a mixing bowl of an electric mixer fitted with a whisk attachment. Beat at medium speed. When the cream becomes thick, add in the ¼ cup of powdered sugar. Whip until soft peaks.
Place the whipped cream in the center of the cake first and using a spatula, spread to the edges.
For the chocolate shavings: Using a vegetable peeler, make shavings of the chocolate bar. Garnish as desired.