Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius). Line a nine- by 13-inch (20- by 30-centimeter) pan with Gefen Parchment Paper.

In a medium bowl, beat egg whites, adding one at a time, on low speed until frothy. Add salt and turn to high speed, then add sugar gradually until stiff peaks are almost formed. Decrease speed and add yolks, oil, and lemon juice, alternating with potato starch. Fold in the grated chocolate. Pour into prepared pan and bake for 25 minutes or until golden. Cool completely before pouring mousse on.

For the mousse: Melt both chocolates and coconut oil in the microwave, at 30-second intervals, until smooth. Meanwhile, beat eggs and sugar at high speed until light and lemon-colored. (No need to wash the mixing bowl after preparing the base.) Fold in melted chocolate mixture. Add coffee liqueur and mix until incorporated. Refrigerate until base is cooled completely. Pour over base and freeze.

Once frozen, cut into circles with a cookie cutter or into squares or fingers.

For the garnish: Drizzle melted chocolate onto a piece of parchment paper to form desired shapes. Allow to harden, then store in an airtight container until ready to use.