1. Prepare 1 day but not more than 3 days ahead. In medium-size bowl, sprinkle yeast over warm water. Let stand until foamy, about 5 minutes. Stir to dissolve yeast. Stir in bread flour. Cover with clean kitchen towel. Let ferment at room temperature, 1 to 3 days; stir mixture twice a day. Starter will be bubbly and pleasantly sour-smelling. (See Note.)Dough:
2. In large bowl, sprinkle yeast over warm water. Let stand until foamy, about 5 minutes. Stir to dissolve yeast. Add 1 cup starter, the rye flour, 1 cup bread flour and salt to yeast mixture. Stir in walnuts and 1-1/4 cups bread flour to form dough.
3. Turn dough out onto lightly floured surface. Knead until smooth and elastic, 10 minutes, adding more flour as needed to prevent sticking.
4. Oil large bowl; add dough and turn to coat. Cover with clean kitchen towel. Let rise in warm place 1 hour or until doubled in volume.
5. Punch down dough. Shape into 10-inch oblong loaf. Place on floured, large baking sheet. Cover with towel. Let rise in warm place 45 minutes or until doubled in volume.
6. Heat oven to 425 degrees F. Sift 1 tablespoon flour over dough.
7. Bake in 425 degree F oven 45 minutes until golden and bread sounds hollow when tapped. Remove to rack; let cool. Serve warm or cooled. Makes 1 loaf.Note:
8. To keep starter for a week or so, place the remaining starter in a large jar. Add 3/4 cup all-purpose flour and 1/2 cup water, and then stir to thoroughly blend. Refrigerate.