Base Cake Layer: Preheat oven to 180 degrees C. Grease an Swiss roll cake tin.
Mix together the walnuts, cinnamon and sugar in a medium bowl and set aside. In a small bowl, dissolve the yeast and sugar in warm water. Let stand until creamy, about 10 minutes.
In a large bowl, stir together the yeast mixture, egg yolks, sour cream and butter. Gradually stir in the flour until the dough becomes too stiff to use a spoon. Use your hand to knead the dough in the bowl until it becomes smooth, about 5 minutes.
Divide the dough into three equal parts, form into balls, cover and set aside to rest for about 15 minutes.
Roll one of the balls of dough between 2 sheets of baking paper to fit the cake tin. Place the dough in the bottom of the prepared cake tin and spread with 3/4 of the nut mixture.
Roll out another ball of dough in the same way, place this over the nut layer in the pan and spread the apricot preserves evenly over the dough. Roll the third ball in the same way and place on top of the layer of preserves.
Place the cake in the preheated oven and set the timer for 40 minutes. When the timer goes off, the top of the cake should be golden brown, if not then wait a few minutes.
Meringue Layer: Place the egg whites into a clean glass or metal bowl. Whip the egg whites to soft peaks, then gradually add the sugar while beating the egg whites to stiff peaks.
Spread the meringue evenly over the top of the cake and sprinkle with the remaining nut mixture.
Bake the meringue covered cake for an additional 15 minutes. Cool in the cake tin set on a wire rack. Trim the edges for a cleaner presentation. Serve at room temperature.