To prepare starter, combine buttermilk or water and 1 cup rye flour in a quart jar.
Cover and allow to stand at room temperature for 4 days.
Stir once or twice daily.
To prepare bread, pour warm water into Bosch mixing bowl.
Sprinkle yeast over water, and allow to activate.
Add starter.
Stir in salt, buttermilk or water, rye flour, and whole wheat flour.
Knead 10 to 12 minutes.
Cover and let rise 1 1/2 hours.
Brush baking sheets with shortening, and sprinkle with cornmeal.
Divide dough into two equal portions.
Shape into long French loaves, and place on baking sheets.
Let rise 15 to 20 minutes.
Brush lightly with beaten egg white, and sprinkle with sesame seeds.
Slash top diagonally three or four times.
Let rise until double.
Place in an unheated oven, set temperature at 400° F.and turn on oven.
Bake 15 minutes, then reduce heat to 350° F.and bake an additional 25 to 30 minutes.
Remove from baking sheets, and cool on cooling rack.
NOTE: All-purpose flour may be used instead of or in combination with the whole wheat flour.
A tablespoon of caraway seeds may be added with the buttermilk or water for a rich caraway flavor.