Preheat oven to 325°.
Lightly grease two 9” square cake pans and line with parchment.
Melt chocolate and set aside to cool to room temperature.
In a separate bowl, whisk together the almond flour, potato flour and salt. Set aside.
With the whisk attachment, whip the butter and 150 grams sugar at medium speed until the mixture is light and has lightened in color. Add cooled melted chocolate and mix well. Turn mixer down to low speed and add yolks 1 – 2 at a time, mixing well after each addition. Stopping to scrape down bowl as needed.
Stir in almond flour mixture until well combined.
In a separate bowl, whip egg whites until frothy and soft peaks begin to form. Begin to add 150 grams of sugar one tablespoon at a time and continue to beat until stiff peaks form being careful not to over whip, the whites should be glossy.
Using a large spatula, gently fold one fourth of the egg white mixture into the chocolate mixture. Continue to fold in the remaining egg whites; the batter will be much lighter.
Bake at 325° for 30-35 min. Do not open the oven door during cooking as the cake could possibly collapse.
When the cake is done, remove from the oven and run a knife around the edges. Let the cake cool completely before removing from pan. Serve with a dollop of Mascarpone Cream.