Heat oven to 350 degrees. Butter an 8-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 medium bowl, beat butter with a wooden spoon or rubber spatula until soft and creamy; set aside. In bowl of an electric mixer fitted with the whisk attachment, combine remaining 1/2 cup sugar, eggs, and kirsch on medium speed until light, fluffy, and doubled in volume, 7 to 8 minutes. Place 1 tablespoon egg mixture into beaten butter, and mix with rubber spatula.
Sprinkle one-third of the ground nut mixture over beaten eggs, and gently fold in. Repeat process, folding in remaining nuts in 2 batches. Add reserved butter mixture, and fold in evenly.
Pour batter into prepared pan and 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.