In a large mixing bowl, place the water, sourdough starter, bread flour, rye flour, and salt. Stir with a rubber spatula, incorporating all the ingredients and pressing the, into a sticky dough ball. (Alternatively, you can do this in a stand mixer fitted with a dough hook.)
Once the dough has formed a ball, set it in the bowl and cover with plastic wrap. Allow it to rise for 10 to 12 hours, or until doubled in bulk.
Turn the dough out onto a floured work surface. Form it into a smooth dough ball, pulling the sides into the center, until the dough is tight.
Sprinkle some rice flour into the cloth liner of the banneton. Place the dough ball seam side up in the banneton. Cover with a cloth and allow to rise another hour.
Preheat the oven to 425 degrees. Cut a circle out of parchment paper, large enough to cover the bottom of your Dutch oven and go up the sides.
Invert the dough ball onto the parchment paper. With the lame or a very sharp knife, cut a deep slash into the bread, about 1/4-inch deep. Add decorative slashes if you prefer.
Using the parchment paper as a sling, transfer the dough ball to the Dutch oven. Cover and place in the oven.
Bake covered for 25 minutes. Remove the lid and bake an additional 20 minutes.
Remove the Dutch oven from the oven and remove the boule to a rack to cool. Once cooled, slice and serve.
The bread is best the day it is baked, however, it should be good for sandwiches and toast for the next couple days when stored in an airtight container at moderate temps.Remember there are no preservatives in this bread. At high heat, the bread will go stale or moldy within a few days.For longer storage, slice and wrap well and store in the freezer.For sourdough rye bread with caraway, add 1 tablespoon caraway seeds when mixing the dough.Nutritional values are approximate and based on the loaf being sliced into 12 slices.