1/2 c. (1 stick) butter, cut into pieces
1/2 c. sugar
1/2 tsp. salt
1 env. dry yeast
1/4 c. warm water
1 lg. egg, beaten to blend, room temperature
4 c. (about) unbleached all-purpose flour
1 lg. egg, beaten with 2 tbsp. water (glaze)
Add yeast mixture and 1 beaten egg to milk mixture. Stir in enough flour, 1/2 cup at a time, to form soft, slightly sticky dough. Lightly grease large bowl. Add dough, turning to coat. Cover bowl with kitchen towel and let dough rise in warm draft-free area until doubled in volume, about 2 hours.
Grease two heavy large cookie sheets. Turn dough out onto lightly floured work surface and knead until smooth, 2 minutes. Divide dough in half. Divide each half into 3 pieces. Roll each piece out between hands and floured surface to 18 inch long rope.
Arrange 3 ropes side by side on 1 prepared sheet. Braid ropes. Pinch ends together and tuck under loaf. Repeat process with remaining 3 ropes on second cookie sheet for second loaf. Cover each loaf with kitchen towel and let rise in warm draft-free area until almost doubled in volume, about 1 hour.
Preheat oven to 350 degrees. Brush egg glaze over loaves. Bake until loaves are golden brown and sound hollow when tapped on bottom, about 25 minutes. Transfer to racks and cool.