Heat the beer to 105 to 115 F. and pour 1/2 cup into a small bowl. Stir in the yeast and let stand 10 minutes.
Mix the flours, sugar and salt in a large bowl. Make a well in the center. Pour the yeast mixture, oil and remaining 1 cup beer into the well and stir until blended.
Knead dough on a floured surface until smooth and elastic, about 10 minutes, adding more flour if necessary.
Coat a large bowl with walnut oil. Place the dough in the bowl and turn to coat with oil. Cover with a damp towel and let rise in a warm place until doubled in bulk. (You can also let the dough rise overnight in a cool place or in the refrigerator.)
Punch dough down and knead in the onion and walnuts until evenly distributed throughout the dough.
Divide dough in half. Divide each half into thirds. Using your hands, roll each of the pieces into 12" long ropes. Braid 3 ropes together to form a loaf. Tuck the ends under and place on an 18 x 12" baking sheet. Repeat with remaining dough, placing it on the same baking sheet. Cover and let rise until doubled in bulk, 45 minutes to 1 hour.
Beat the egg and 2 tsp. Water in a small bowl. Brush the tops of the loaves with the egg wash and sprinkle with rosemary. Bake at 375 F. until crusty and brown, 45 to 50 minutes. Cool in the pans for 10 minutes. Turn out onto wire racks and cool completely.
The authors write: "A hearty and rustic bread that makes an excellent picnic lunch with cheese, especially goat's milk cheese. Take your favorite full-bodied red wine along."
From _The Silver Palate Good Times Cookbook_ by Julee Rosso and Sheila Lukins. New York: Workman Publishing Company, Inc., 1984. Isbn 0-89480-831-1. Pp. 232-233. Electronic format by Cathy Harned.