In a stand mixer attached with a dough hook, combine all ingredients except for butter. Knead until it comes together in a ball of dough.
Add butter. Knead until it is fully incorporated into the dough, approximately 3½ minutes.
Pause to do a windowpane test. Pinch a small piece of dough — gently stretch dough in opposite directions to resemble a windowpane without it breaking or tearing, the gluten is sufficiently developed. If not, continue to knead another 3-5 minutes and do another windowpane test.
Divide dough into 2. Add cocoa paste (cocoa powder mixed with hot water) to 1 dough and knead to get a brown dough. Place the 2 dough in 2 deep bowls and proof in a warm place (turned off oven with a bowl of hot boiling water placed on oven floor) for 50-60 minutes.
Degas both doughs and roll into 2 rectangular. Stack dough as per video and roll into a single rectangular. Roll from top like a Swiss roll and seal the ends.
Prepare a Pullman baking tin. Place it seal side down, into the baking tin. Cover and proof in a warm place for 45 minutes-1 hour until dough reaches 90% of tin capacity, a few inches below the rim.
Dust with flour and bake in a preheated oven Meanwhile, preheated oven of 180°C for 30-35 minutes.
