In the bowl of a stand mixer, mix the yeast with milk and sugar and 1/3 cup of the flour. Let rest until small bubbles appear and break the surface, about 10 to 15 minutes.

With the mixer fitted with the dough hook, on low speed, mix in the 6 tablespoons butter then the egg and salt. Gradually add the flour until it’s incorporated. Turn the mixer to medium-high speed and knead the dough until smooth, about 5 minutes.

(Note: If dough it too loose/sticky, add more flour, 1 tablespoon at a time)

Cover the bowl with a kitchen towel or plastic wrap and refrigerate the dough for 6 hours, or overnight, or roll out in the next step.

(Note: Dough get better with time but if you want to make it immediately you can do so)

Butter a 9-inch (23cm) loaf pan and line the bottom and up the sides with a piece of parchment paper overhanging the two long sides, which will help you remove the baked babka later. this may not be needed if you choose alternative babka shapes.

To make the filling, melt the 7 tablespoons of butter in a medium saucepan. Add the sugar and stir until dissolved or almost completely dissolved. (It’s okay if there are grains of sugar visible – they’ll melt later.) Remove from heat and add the chocolate. Let stand 1 minute, then stir until the chocolate is melted and smooth. Stir in the cocoa powder and cinnamon. Set aside.

On a lightly floured surface, roll the dough (chilled or at room temperature) to a rectangle 30 x 50cm (12 x 20-inches). You can use ruler or measuring tappet help you out. If the dough resists when rolling it, let it sit 5 to 10 minutes, then continue to roll it out to the final dimensions.

Spread the chocolate filling over the surface of the rectangle all the way to the edges. Strew the nuts and cookie (if using) over the chocolate. In the picture above nuts were omitted and a layer of dulce de leche was also spread over the chocolate (you can start to get creative with your fillings). Starting at one of the long ends of the rectangle, roll up the dough tightly so you have a log that’s 50cm (20 inches) long.

Using a sharp knife, slice the dough completely in half lengthwise. With the cut sides facing up, overlap the end of one cut half over the other (with the cut sides still facing up), then take the other cut half and fold it over the other, making sure the cut sides are always facing up. Continue making a rope-like formation overlapping and twisting the two halves of the dough together until the dough into one big twist. Any nuts or filling that have fallen out, toss into the bottom of the loaf pan. For a good resource for folding your babka check here.

Lift the twisted loaf and squidge it into the prepared loaf pan by pushing in on the two ends, so it fits in nicely. If shaping into circular babka, this bakes nicely in a foil lined cast iron.

Put the loaf pan in a very warm place, such as near a radiator or in an oven turned off, and let rise for about two hours, until it’s puffy and almost doubled in size.

While the dough is rising, make the syrup by bringing the water, sugar to a boil in a small saucepan. Let boil for 4 minutes, skimming off any foam that rises to the surface with a spoon. Remove from heat and set aside.

Fifteen minutes before you bake the babka, preheat the oven to 375ºF (190ºC). Bake the babka on the middle rack of the oven for 30 minutes, or until a skewer inserted into the center (in a part where there is less chocolate filling), comes out clean of dough. There may be some bits of chocolate clinging to it, which are normal.

Remove the babka from the oven and brush the room temperature syrup over the babka. Let cool completely before lifting the babka out, do not try to remove it or slice it while it’s warm, or it will break.

Serve the babka sliced. It will keep for up to 4 days at room temperature or can be frozen for up to two months, if well-wrapped.