Preheat oven to 350 degrees F.
Butter a 9-inch round pan, and line with parchment paper. Butter paper, and lightly dust with flour. Place 1 cup walnuts and 3 tablespoons sugar in a food processor, and finely grind. Transfer to a bowl. Sift flour over nut mixture. Mix well to combine.
In a medium bowl, beat butter with a wooden spoon until soft and creamy; set aside. In the bowl of an electric mixer fitted with the whisk attachment, combine 1/2 cup sugar, the eggs, and Kirsch on medium speed until light, fluffy, and doubled in volume, 7 to 8 minutes. Place 1 tablespoon egg mixture into the beaten butter, and mix with a rubber spatula.
Sprinkle 1/3 of the ground nut mixture over the beaten eggs, and gently fold in. Repeat process, folding in remaining nuts in 2 batches. Add reserved butter mixture, and fold in evenly.
Bang prepared pan lightly on work surface to remove trapped air bubbles, then pour batter into prepared pan. Bake until cake pulls away from sides of pan, about 30 minutes. Cool on a rack.
Heat jam and cognac in a small saucepan over medium heat to liquefy. Strain through a fine sieve, and cool slightly.
Transfer cake, right side up, to a serving plate or pedestal. Tuck paper under edges of cake. Pour glaze onto cake. Using an offset spatula, spread glaze over top and sides of cake. Remove paper. Serve with whipped cream.
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