Rye starter:
1 cup starter
3/4 cup rye flour (*2)
1/4 cup bread flour (*2)
1 cup water
Dough;
1 tsp. Dry yeast (*1)
1 T. Kosher salt
2 T. brown sugar
1 T. molasses
1 cup water
Swirl:
1 T. cocoa powder
1/2 T. espresso powder
Additional bread flour
4x13 Pullman pan
Kitchenaid with dough hook
This bread often has caraway seeds on top.
Day 1: Take 1 cup of your starter and make the rye starter. Cover and let sit for several hours or overnight. (*3)
Into the starter, add the water, molasses, salt, sugar, and yeast. Mix thoroughly.
Divide the dough into two bowls. To one bowl, stir in the cocoa powder and espresso powder.
Incorporate a little bread flour at a time into each bowl until they form a loose, doughy ball. Turn out onto a lightly floured board. 
Knead each, adding just enough flour to prevent sticking, just until you can make a ball. Rye dough won’t make a springy ball, and never completely loses its stickiness.
Place into two lightly oiled containers and let rise until double, anywhere from 2 hours to 5 hours.
Turn the light dough out onto your floured board. Press and stretch out into a rectangle. Repeat with the dark dough.
Swirl:
Put the rectangle of dark dough on top of the light. Roll up tightly and pinch the seam into the roll. Trim up your ends.
Marble:
Put the rectangle of dark dough on top of the light. Roll up tightly and pinch the seam into the roll. Cut down the length of the roll. 
Twist the two pieces together, pinch together the ends. Trim up your ends.
Put in your pan, and press out. 
Spritz with water and cover with the lid.
Let the bread rise until a half inch from the top or if you added yeast, 1 inch, 1-4 hours. (From the knuckle to the tip of your thumb is about 1 inch).
Preheat the oven to 350 degrees.
When you check on the loaf, if it is doming and not spreading into the sides, snip a few cuts in the center. This will force it to spread more. 
If the dough has risen too much and is touching the lid, use scissors to snip excess off across the top and discard. This is more likely to happen if you add dry yeast. If it is already touching the lid when it goes it, dough will be squeezed out the openings.
Spritz with water and close the lid.
Bake for 45 minutes.
Remove the loaf to a cooling rack.

*1 This dough is a slow riser. If you don't have dry yeast to give it a boost, expect it to take longer.
*2 The original recipe calls for 1 cup of rye in the starter.
*3 If you don’t plan to make bread right away, mix the starter and put it in the fridge. Let it warm and become bubbly before using.