Line the bottom and sides of an 8 x 4 -inch loaf pan with a double layer of waxed paper, folding the paper to fit smoothly. In a small bowl, stir together walnuts and 1/4 cup of the blueberry preserves; set aside. Spoon orange sorbet into the lined pan, smoothing the top to make an even layer. Spread the reserved walnut-preserves mixture evenly over the orange sorbet. Spoon the lemon sorbet evenly over the preserves and smooth the top. Cover tightly with aluminum foil. Freeze several hours or overnight. Just before serving, in a medium bowl, stir remaining 2 tablespoons preserves until smooth; fold in fresh blueberries. Invert the cake onto a chilled serving plate. Remove the pan and waxed paper; spoon about one-fourth of the blueberry mixture down the center of the cake. Cut the cake into 8 (1-inch) slices. Serve on chilled dessert plates; top each slice with a spoonful of the remaining fresh berry mixture. Serve immediately.

Yield : 8 portions