In the bowl of your stand mixer, add warm milk, cream, cocoa and flour. Knead on low speed until flour is well incorporated (2-3 minutes). Cover and rest for 45 minutes to 1 hour.
Add yeast, sugar and salt. Mix on low for 3 minutes and medium speed for 3 minutes.
Go back to low speed and add the butter little by little. Continue kneading for 8-10 minutes until smooth and the butter fully incorporated.
Place the dough in a lightly oiled bowl, cover, and let rise in a warm spot (25-28°C) for 1.5-2 hours until almost doubled.
Roll the dough into a 55 × 40 cm rectangle.
Spread the custard evenly and then the chocolate chips.
Fold the dough twice and place in the freezer for 5-10 minutes.
Slice into long strips (7-8 for extra large buns).
Twist each strip several times and shape into a roll. Place on baking paper lined trays and let rise in a warm place for 60-75 minutes, until puffy.
Preheat your oven to 175°C. Gently brush the buns with the egg wash.
Bake for 18-22 minutes until slightly golden (cover with foil if the buns get brown too quickly).
Optional: brush with syrup (2 tsp sugar mixed with 2 tsp boiling water) for a glossy finish while still hot.
