Bolo Polana

Ingredients

 * 3 medium-sized boiling potatoes (about 1 pound), peeled and quartered
 * 2 tablespoons plus 3 quarter-pound sticks unsalted butter, softened
 * 2 tablespoons flour
 * 2 cups sugar
 * 2 cups roasted unsalted cashews, finely chopped or pulverized in a blender or with a nut grinder
 * 2 teaspoons finely grated fresh lemon peel
 * 2 teaspoons finely grated fresh orange peel
 * 9 egg yolks
 * 4 egg whites

Directions

 * 1) Drop the potatoes into enough boiling water to cover them completely and cook briskly, uncovered, until they are soft enough to be easily mashed with a fork. Drain, then mash the potatoes vigorously with a fork or put them through a ricer set over a bowl. Set the potatoes aside to cool to room temperature.
 * 2) Preheat the oven to 350°F. With a pastry brush, spread 2 tablespoons of the softened butter evenly over the bottom and sides of a spring form cake pan 9 inches wide and 3 inches high. Sprinkle the pan with the flour, tipping it from side to side to spread the flour evenly. Then invert the pan and rap it sharply to remove the excess flour.
 * 3) In a deep bowl, cream the 3 sticks of softened butter and 2 cups of sugar together by beating and mashing them against the sides of the bowl with the back of a spoon until they are light and fluffy. Beat in the potatoes, cashews, lemon peel and orange peel.
 * 4) Add the egg yolks, 1 at a time, stirring after each addition, and continue stirring until the mixture is well blended.
 * 5) With a wire whisk or a rotary or electric beater, beat the egg whites until they are stiff enough to form firm, unwavering peaks on the beater when it is lifted from the bowl. Stir a heaping tablespoon of the whites thoroughly into the potato mixture. Then spoon the remaining egg whites over the mixture and, with a rubber spatula, fold them together gently but thoroughly.
 * 6) Pour the batter into the buttered and floured pan, spreading it and smoothing the top with the spatula. Bake in the middle of the oven for about 1 hour, or until the top is brown and a skewer inserted into the middle of the cake comes out clean. Let the cake cool for 5 minutes.
 * 7) Then remove the sides of the pan and with the help of a large metal spatula slide the cake off the base onto a wire rack. Serve the bolo Polana while it is still slightly warm, or let it cool to room temperature before serving.