Combine bubbly sourdough starter and warm water in your stand mixer bowl. Combine remaining ingredients and mix using the dough hook set on medium for about 10 minutes or until dough is fully combined.
Remove from stand mixer bowl, form into a ball and place in a separate bowl and cover with plastic wrap. Let sit in a warm area for 30 minutes.
Perform the stretch and fold process: Every 15 minutes stretch and fold each side of dough, then place back in bowl, rest and repeat 4 times.
On a floured counter, roll out dark sourdough rye into a rectangle about 5" x 8" , then roll out light sourdough rye into the same size rectangle.
Place the light sourdough rye rectangle on top of the dark sourdough rye. Roll out just enough to press the two gently together. Using your hands, starting with the long edge furthest from you, roll the dough towards you, tucking as you go as tight as you can get it. Place in a greased 5" x 9" bread pan. Cover and let rise on counter overnight.
In the morning, place in the refrigerator for 1-2 days. When ready to bake, remove and let sit on counter while oven pre-heats to 400 degrees. Using a very sharp knife, make a few slashes on top of loaf. Cover loosely with foil. Bake for 15 minutes at 400 degrees, then reduce to 350 degrees and bake for an additional 20 to 25 minutes. Remove foil and bake for 5 minutes or until internal temperature is 200 degrees when measured with a digital thermometer.
Remove from oven, gently remove loaf from pan to a wire rack. Let cool completely before slicing.