In a large bowl, dissolve yeast in warm water. Let stand until foamy, 5 to 10 minutes. Stir the warm milk, orange juice, sugar, ricotta cheese, orange zest, salt and egg into yeast mixture. Mix at low speed 2 cups flour into the yeast mixture until a wet dough forms. Beat in the remaining flour, 1/2 cup at a time, until a stiff dough forms. Turn dough out onto a lightly floured surface and knead until smooth and elastic, about 5 to 10 minutes, adding more flour as needed to prevent sticking. Place the dough in a large greased bowl, turning to coat. Cover loosely with a damp cloth and let rise in warm place until doubled, about 1-1/2 hour.

Grease a 10 inch spring form pan. Punch down dough. Turn out onto a lightly floured surface and knead for 1 to 2 minutes. Divide the dough into 3 equal pieces. Roll each piece into a 20 inch long rope. Braid the ropes together. Coil braided dough in prepared pan; tuck ends under. Cover loosely with a damp cloth and let rise in warm place until almost doubled, about 30 minutes. Preheat oven to 425°F Brush the dough with glaze. Bake until the top of the cake is golden brown, 25 to 30 minutes. Turn the cake out onto a wire rack to cool slightly.

Top prepare icing, in a small bowl, stir together powdered sugar and orange juice until smooth. Spread icing over warm cake. Serve warm.