In a large bowl, dissolve yeast in 1/2 cup warm water. Add 1 cup sugar, 1/2 cup butter, salt, egg, egg yolk and remaining water. Beat until blended. Add 4 cups flour. Beat until smooth. Stir in enough remaining flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, 6-8 minutes. Place in a greased bowl, turning over once to grease top. Cover and refrigerate for 8 hours.
Punch dough down. Turn onto a lightly floured surface; divide into thirds. Roll each piece into a 16x10-in. rectangle. Spread remaining melted butter over dough. Combine the chopped almonds, lemon zest and remaining sugar; sprinkle over butter. Roll up jelly-roll style, starting with a long side; pinch seams and ends to seal. Place seam side down on greased baking sheets. With a knife, cut loaves in half lengthwise to within 1 in. of one end. Holding the uncut end, loosely twist strips together. Cover and let rise until doubled, about 1-1/2 hours.
Bake at 350° for 25-30 minutes until bread sounds hollow when tapped. Remove from pans to wire racks. Combine the confectioners' sugar, lemon zest, extract and enough milk to achieve spreading consistency; spread over warm bread. Sprinkle with toasted almonds.