Soak the yeast in the warm (105 degrees-115 degrees) water until dissolved. Add the sugar. Mix well. Heat the sour cream until warm. Add= to the yeast mixture along with the lemon rind and salt. Beat in the first measure of eggs. Add enough of the flour to make a soft dough. Beat the butter into the dough. Turn the dough onto a floured board and knead until smooth (6-7 minutes). Place the dough in a lightly buttered bowl. Cover tightly with plastic wrap. Let rise until doubled in bulk (45-60 minutes). Punch down. Roll out on a floured board to form an 46 cm x 30 cm rectangle. Spread the lemon curd on the dough, leaving a 2 cm border on all sides. Carefully roll up the dough. Slice into 9 cm thick slices. Place the rolls in a well greased (8 inch) pie pan in a circle. Let rise for about 30 minutes. Preheat oven to 360=B0. Lightly beat the second measure of egg. Brush the cake with the beaten egg. Sprinkle with nuts. Bake for about 30 minutes.