In a large mixing bowl, add active sourdough starter and room temperature Guinness. Mix with a Danish dough whisk or your hand until it looks like a brown, milky liquid.

To a separate bowl, add the bread flour, rye flour, cocoa powder and salt. Whisk until evenly combined. Then pour the dry ingredients into the wet ingredients. Be sure to mix until all of the flour is incorporated. The dough will look shaggy, not like a uniform dough ball.

Cover the bowl with plastic wrap and let the dough rest for at least 30 minutes before you move on to the next step.

With slightly wet fingers, scrape the dough away from the bowl. Grab a section of the dough and stretch the bread dough above your bowl. Then fold over on top of the dough. Rotate your bowl clockwise a quarter of the way and repeat identical stretch and fold. Repeat the process until you come full circle, about 4-6 times. Cover the dough again and let it rest for another 30 minutes.

Repeat the identical stretch and fold three more times (for a total of 4 different rounds), waiting at least 30 minutes between each stretch and fold. Cover the dough after each stretch and fold.

Once you have completed the final set of stretch and folds, cover the dough and let it rest for the remainder of the bulk fermentation on your counter, about 7-9 more hours if the dough is kept at 68-70 degrees F.

With slightly wet fingers, gently release the dough from the sides of the bowl. Be careful not to pop all of those lovely bubbles! Tilt the bowl and leave gravity to do the work to move the dough on the counter. Shape the dough by doing another round of stretch and folds until you have gone full circle. With a bench scraper or your hands, turn the dough upside down, so the seam is now on the counter. Cover the dough with the bowl and let it rest for 30 minutes.

While you are waiting for the dough to rest, prepare your proofing basket. This can either be a banneton or a small mixing bowl lined with a damp tea towel.

After 30 minutes of rest, flip the dough, with the seamed side up. Gently pull the bottom of the dough towards you, then fold it towards the center of the dough. Pull the right side of the dough out and fold towards the center. Repeat with the left side. Finally, stretch the top of the dough away from you and fold towards the center of the dough. Flip the dough over again, seam side down.

Gently cup your hands around the dough ball. Turn the ball in a clockwise motion about a quarter turn and then softly pull the dough towards you. Do this repeatedly until you see the dough form a tighter and more round shape. Stop if the dough starts to tear.

With a bench scraper or just your hands, carefully scoop up the dough and lay it upside down (seed side up) into your floured proofing basket and cover it with a plastic bag or a shower cap.

Place your proofing basket in the fridge to cold-proof for 8-72 hours.

30 minutes before baking, place the dough in the freezer. This will tighten up the dough which helps with the scoring design. At the same time, place your Dutch oven in your oven and preheat to 500 degrees F. Allow the Dutch oven to preheat for at least 30 minutes.

Place a piece of parchment paper on your workspace and gently flip the banneton upside down over the parchment paper. Since you dusted the banneton, your dough should slowly release and fall onto the parchment paper, landing in the middle with the floured side facing up.

With a lame / razor blade or sharp knife, score a crescent moon shape on top of the dough.

Grab the corners of the parchment paper and carefully place the Guinness dough into your preheated Dutch Oven and cover with the lid.

Lower the oven to 450 degrees F and bake the bread covered for 30 minutes. Then remove the lid of the Dutch oven and continue to bake the bread for an additional 15-20 minutes with the lid off at 425 degrees F or until the internal temperature reaches 205 degrees F.

Once golden brown, remove the Dutch oven from your oven. Using the corners of the parchment paper, lift the sourdough bread out of the Dutch oven and place it onto a wire rack to cool.

Allow your homemade bread to cool for at least 1 hour before cutting into it.