Combine 1 cup hot water, raisins, and currants in a bowl. Cover and let stand 10 minutes or until raisins and currants plump. Drain and set aside.
Dissolve 1 tablespoon sugar, saffron, and yeast in warm milk in a small bowl; let stand for 5 minutes. Lightly spoon flour into dry measuring cups; level with a knife. Combine 3 cups flour, remaining 3 tablespoons sugar, salt, and cinnamon in a large bowl. Add raisins, currants, yeast mixture, butter, and 1 egg to flour mixture; stir until dough forms.
Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 10 minutes); add enough of remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands.
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in size. (Gently press two fingers into dough. If indentation remains, dough has risen enough.) Punch dough down. Turn out onto a lightly floured surface; knead 3 times.
Divide dough into 3 equal portions, shaping each portion into a 16-inch rope. Place ropes lengthwise on a baking sheet coated with cooking spray (do not stretch); pinch ends together at one end to seal. Braid ropes; pinch loose ends to seal. Cover and let rise 1 hour or until doubled in size.
Preheat oven to 375°.
Lightly beat remaining egg in a small bowl. Gently brush dough with egg. Bake at 375° for 25 minutes or until loaf sounds hollow when tapped. Remove from pan; cool on a wire rack.