In a large bowl, beat egg yolks and 1/2 cup sugar until thickened. In a small bowl, beat egg whites until foamy. Gradually beat in remaining sugar, 1 tablespoon at a time, on high until stiff peaks form. Fold into yolk mixture. Gradually fold in flour.
Divide batter among three greased and floured 9-in. round baking pans. Bake at 350° for 15 minutes or until golden. Cool in pans for 5 minutes before removing to wire racks to cool.
For buttercream, in a small saucepan, whisk the sugar, eggs, yolks, vanilla and coffee. Add chocolate; cook and stir over low heat until thickened (do not boil). Cool completely.
In a small bowl, cream butter until light and fluffy. Gradually add chocolate mixture; set aside. Finely chop apricots; drain and place in a bowl. Stir in preserves; set aside.
Split each cake into two horizontal layers; place one on a serving plate. Spread with 2/3 cup buttercream. Top with a cake layer and 2/3 cup apricot filling. Repeat layers twice. Cover and refrigerate 3 hours before serving. Garnish with chocolate curls.