Dissolve the yeast in warm water in a large bowl; let stand 5 minutes. Lightly spoon flours into dry measuring cups, and level with a knife. Add rye flour and parsnip to yeast mixture, and stir well to form a sponge. Cover and let rest at room temperature for 30 minutes.
Add 2 cups bread flour, caraway seeds, 1 teaspoon salt, and pepper to parsnip mixture; stir until a soft dough forms. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 8 minutes); add enough of remaining bread flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
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, 45 minutes or until doubled in size. (Gently press two fingers into the dough. If indentation remains, dough has risen enough.) Punch dough down, and lightly spray surface of dough with cooking spray. Cover and let rise a second time, 45 minutes or until doubled in size. Punch dough down; cover and let rest 5 minutes. Shape dough into an (8-inch-long) oval; place on a baking sheet sprinkled with cornmeal. Lightly spray surface of the dough with cooking spray. Cover and let rise in a warm place (85°), free from drafts, 30 minutes or until doubled in size.
Preheat oven to 400°.
Combine 1 teaspoon water and egg white, and brush over loaf. Sprinkle loaf with kosher salt. Bake at 400° for 30 minutes or until the dough is browned on bottom and sounds hollow when tapped. Cool on a wire rack.