Preheat the oven to 350°F (175°C). Grease an 11x17-inch jelly roll pan.

Combine walnuts, ¾ cup sugar, and cinnamon in a medium bowl; set aside.

Dissolve yeast and 1 teaspoon sugar in warm water in a small bowl. Let stand until it forms a creamy foam, about 10 minutes.

Stir yeast mixture, butter, sour cream, and egg yolks together in a large bowl. Gradually mix in flour until the dough becomes too stiff to stir, then knead until smooth, about 5 minutes. Divide dough into 3 equal balls, cover and let rest for 15 minutes.

Roll out 1 dough ball between 2 sheets of waxed paper to fit the jelly roll pan. Transfer to the prepared pan and spread with ¾ of the nut mixture. Repeat for the second ball of dough and layer on top, then spread apricot preserves evenly over this layer. Roll out the last dough ball and cover the apricot layer.

Bake in the preheated oven until the top is golden brown, about 40 minutes.

Beat egg whites to soft peaks. Gradually add sugar and beat until stiff peaks form. Spread meringue evenly over the top of the baked torte, then sprinkle with remaining walnut mixture.