In the bowl of a stand mixer, combine all the dough ingredients except the butter. Mix on low speed until there is no dry flour left. Gradually add the butter, one tablespoon at a time.
Scrape down the bowl, cover it with plastic wrap or a damp towel, and let it rest for 30 minutes. Then, do 2–3 sets of stretch and folds, with 30 minutes between each set.
Let the dough rise until it increases by about 50% in size (not doubled). This usually takes 6–8 hours at 72°F (22°C). Cover it tightly and refrigerate overnight.
The next day, melt the butter and chocolate chips together over low heat. Once melted, remove from heat and stir in the cocoa powder and sugar.