Dissolve yeast and 1 1/2 teaspoons sugar in warm water; let stand 5 minutes.
Combine milk, salt, shortening, butter, and remaining sugar in a large bowl; stir until sugar dissolves. Cool to lukewarm (105° to 115°). Add yeast mixture and 3 eggs, stirring well. Add 4 cups flour; beat well.
Stir in remaining flour to make a soft dough. Turn dough out onto a lightly floured surface; knead 5 minutes. Place in a greased bowl, turning to grease top. Cover and let rise in a warm place (85°), free from drafts, 50 minutes or until doubled in bulk.
Punch dough down, and let rest 5 minutes. Divide dough into 3 equal portions. Roll each portion into an 18-inch rope. Shape each rope into a loose coil in three greased 8-inch round cake pans, beginning at outer edge of pan.
Cover and repeat rising procedure 50 minutes or until doubled in bulk. Gently brush loaves with 1 egg and sprinkle with sesame seeds. Bake at 350° for 30 minutes or until golden brown. Cool loaves 10 minutes on wire racks before removing from pans.