Preheat the oven to 375°F (200°C). Butter an 8-inch (20 cm) cake pan 2 inches (4 to 5 cm) deep and dust with gluten-free flour; set aside.

In a mixing bowl, combine the egg, egg yolk, and half of the sugar. Whisk until the mixture becomes pale and thickens. Whisk in the potato starch.

In another mixing bowl, whisk the egg whites with the remaining sugar to make a meringue. Fold the meringue into the egg, sugar, and potato starch mixture. Fold in the chopped walnuts and pecans. Spread the batter evenly in the cake pan and bake for 25 minutes, until springy to the touch.

To add a touch of sophistication to this cake, drizzle lines of chocolate over it. You may also dust it with confectioners’ sugar.