Preheat the oven to 400 degrees F.
Lightly grease two sheet pans with the 2 teaspoons of butter, and sprinkle with 2 teaspoons of flour. Knock out the excess flour, and set aside.
In a medium bowl, sift together 1/2 cup flour, potato starch and salt. In a separate bowl, beat together the egg yolks and 1/4 cup of the sugar until pale yellow and thick. Add the vanilla to the egg yolks.
In a clean bowl, beat the egg whites to soft peaks. While beating, slowly add the remaining 1/4 cup sugar and beat until stiff peaks form.
Gently fold 1/4 of the egg yolk mixture into the beaten egg whites. Gradually fold the flour and remaining egg yolk mixture into the egg whites. (The batter should be light and fluffy.) Transfer to a pastry bag fitted with a 1/2-inch plain tip. Pipe 4-inch long strips of batter, about 1-inch apart, onto the prepared pans. Sift a generous amount of powdered sugar on the top of the cookies, and bake until golden and set, 8 to 10 minutes. Remove and transfer to a wire rack to cool.
In a large saute pan, melt the remaining 2 tablespoons of butter over medium-high heat. Add the ginger and cook, stirring, for 30 seconds. Add the cherries, lemon juice, and brown sugar and cook, stirring, until the cherries are softened and the sugar is melted, about 4 to 5 minutes. Remove from the heat and add the brandy. Return to the heat and flame the brandy. When the flames subside, remove from the heat.
To assemble the dessert, form a triangle of ladyfingers in the center of 6 dessert plates. Divide the cherries among the 4 plates, in the center of the triangle. Drizzle the sauce over the ladyfingers. Place a dollop of whipped cream on top of the cherries, sprinkle with chopped hazelnuts, and garnish with mint.
Yield: 6 servings