Sprinkle yeast and 1/2 tsp of the sugar over very warm water in a 1 cup measure. Stir to dissolve yeast. Let stand until bubbly, about 10 minutes.
Combine 2 cups of the flour, salt, lemon rind and the remaining sugar in a large bowl; make a well in the middle. Beat eggs and egg yolks in a small bowl just to mix. Pour eggs, yeast mixture and warm milk into well. Stir liquids into flour until smooth. Beat well.
Add softened butter gradually, beating well. Stir in 1 more cup of the flour. Beat until dough leaves the side of the bowl.
Knead on a lightly floured surface; until smooth and elastic, about 8 minutes.
Press dough into a buttered large bowl, turn to bring buttered side up; cover. Let rise in a warm place, 1 1/2 to 2 hours, or until doubled in volume.
While the dough is rising, make Cheese Filling: Beat cream cheese and cottage cheese in a small bowl with an electric mixer until smooth; beat in egg yolk and sugar. Stir in lemon rind.
Make Crumb Topping: Combine nuts, flour, butter, sugar and cinnamon in a small bowl. Grease two 8 x 1 1/2 inch pans.
When dough has doubled, punch down, knead in raisins; divide dough into four equal parts; press two parts into the bottoms and about 1/2 inch up the sides of the prepared pans; spread each with about 1 cup of the cheese filling.
Shape remaining dough into 2 8-inch circles; place on top of cheese filling. Press the handle of a spoon into dough around edges to seal.
Sprinkle half the crumb topping over each. Let rise in a warm place until dough reaches the top of the pans, about 1 hour.
Bake in a preheated 350 F degree oven for 40 minutes; or until the cakes sound hollow when tapped. Cool on a wire rack. (Place foil loosely over the crumb topping; invert onto rack, then turn right side up.) Let cool at least 30 minutes before serving. Sprinkle with powdered sugar.