In stand mixer bowl, add 1 cup bread flour, caraway seeds, and salt; mix well. Add water, oil, molasses and sourdough starter to flour mixture. Using a paddle attachment, blend on medium speed for 4 minutes.
Switch to dough hook attachment. Gradually stir in rye flour enough remaining bread flour to make a firm dough. Knead until smooth and elastic, about 5 to 7 minutes.(NOTE: For hand mixing: following above steps, mix ingredients in large mixing bowl using a wooden spoon or dough whisk. Knead on floured surface until smooth and elastic.)
Place dough in lightly oiled bowl and turn to grease top. Cover; let rise until indentation remains after poking dough with finger down to second knuckle, about 1 hour.
Turn dough onto lightly floured surface; punch down to remove air bubbles. Shape dough into a round loaf. Place on greased cookie sheet sprinkled with cornmeal. Cover; let rise 15 minutes.
Preheat oven to 375°F. (See note below to add steam for a crusty loaf.)
With a sharp knife or bread lame, make 2 or 3 slashes on the top of the loaf. Cover; let rise until indentation remains after lightly touching.
Bake for 40 to 45 minutes. Remove from cookie sheet; cool on wire rack.
For a crusty loaf: Place a metal broiler tray on bottom oven rack before preheating oven. After placing loaf in oven to bake, quickly and carefully pour 1 cup hot water into broiler tray and close oven door. Bake as directed.