In a large metal mixing bowl, add the water, flour, yeast, and oil. Use a wooden spoon to mix the dough by hand until no flour is visible, about 2 minutes. Let the dough rest for 20 minutes.

Warm the chocolate baking bar in the microwave until it has completely melted (about a minute) or use a double boiler (bring an inch of water to a boil in a saucepan, then place a heat-safe bowl on top, add the chocolate and melt it, mixing frequently, about 2 to 3 minutes). Allow the chocolate to cool for 2 minutes.

Meanwhile, add the salt to the dough in a large mixing bowl, turning it over in the bowl and kneading it until the salt disappears (about a minute). Then, add the cocoa powder and repeat the process.

Begin the final 10-minute hand mix. Start in the bowl. Slowly add the melted chocolate into the dough while mixing. Once it is absorbed into the dough (about a minute), turn the dough onto a lightly floured surface and knead with both hands for about 10 minutes. Use the heel of your hand, pressing the dough down hard and out on the counter, then gather the dough up and fold it back into itself. Repeat.

Cut the dough into 2 or 3 even pieces (depending on your preferred size), weigh and ball.

Place the balls in a proofing container (or in lightly oiled containers covered with plastic wrap or lids) and cold-ferment in the fridge for 48 hours. You can continue to cold-ferment for up to 96 hours.