For the Soaker: Combine all the ingredients for the soaker in a medium bowl. Cover with plastic wrap and let sit at room temperature overnight, approximately 8-12 hours.

For the Dough: Combine both flours, yeast and water in a separate bowl. Stir to combine as best you can (mixture will be thick), and then knead briefly with your hands until you have a cohesive mixture. Dough will be very thick and clay-like in texture. Cover with plastic wrap and let sit at room temperature overnight, about 8-12 hours.

Grease a 13 x 4 inch pullman pan with lid (or 2 loaf pans; use glass baking pan/ sheet pan for the lid) with butter and dust with rye flour, including the lid. Set aside. Combine the soaker, flour mixture, salt and molasses in the bowl of a stand mixer. Fit mixer with paddle attachment and mix on low speed for 2-3 minutes until everything is thoroughly combined, scraping down the sides of the bowl from time to time.

Increase speed to medium and mix for an additional 2-3 minutes, stopping to occasionally scrape down the sides of the bowl. Mixture will be quite sticky.

Transfer the dough to the prepared pan. Smooth out the top and sift a thin layer of rye flour over the surface of the dough. Place lid on pan and let the dough rise for 1½ -3 hours at room temperature or until it is about ½ inch from the top of the pan.

Meanwhile, preheat the oven to 500 degrees. Bake the loaf with the lid on for 15 minutes. Reduce the temperature to 400 degrees and continue to bake, covered, for an additional 15 minutes.

Remove the pan from oven and carefully slide the lid off. Reduce the temperature to 325 degrees and bake, uncovered, for an additional 45 minutes.

Remove from the oven and immediately turn the loaf out onto a metal cooling rack set inside a rimmed baking sheet. Return the bread to the oven for an additional 10 minutes.

Remove from the oven and allow the bread to cool completely before slicing, at least 3 hours.