Preheat oven to 350 degrees Fahrenheit. Line two jellyroll pans with Gefen Parchment Paper.

In the bowl of an electric mixer, beat egg whites until foamy. Slowly add in sugar, beating until stiff peaks form. Add potato starch and ground nuts.

Divide batter between pans and use a spatula to spread evenly. Bake until golden, 20–25 minutes.

Combine eggs, yolks, sugar, and lemon juice in a double boiler. Cook, stirring occasionally, until mixture thickens, about 10-12 minutes. Mixture may curdle slightly.

Blend mixture using an immersion blender. (If using a standard blender, blend and return mixture to the pot). Whisk in margarine.

Using a spatula, spread half the cream over one cake. Carefully place second cake over the cream. Spread the remaining cream over the second cake.

Freeze until firm. Slice into squares or bars and serve frozen.

Optional: Garnish with whipped cream.