Combine all of the dough ingredients, mixing until everything is moistened. Cover the bowl, and let the dough rest for 20 minutes (this will shorten your kneading time). Then mix/knead it until it's soft and smooth in a stand mixer or by hand.

Place the dough in a lightly greased, covered bowl and let rise for about 1 hour and then move it to the fridge for 2 hours or up to overnight. It will continue to slowly rise in the fridge and the butter will firm up making it easier to roll out. It should about double in size. 

To make the filling: Melt the butter and mix in the sugar, cinnamon, cocoa, and salt. The mixture will be grainy and thick.

Prepare a large bread pan for baking by buttering the pan and lining it with a piece of parchment. You want the parchment to over hang on the long sides of the pan and to help you lift the bread out once it's done. 

Shape the dough into a 9" x 18", 1/4"-thick rectangle. Don't worry about the exact dimensions too much, but you do want your short end to be the length of the bread pan you plan to use. 

Schmear the dough rectangle evenly with your filling leaving a one inch gap on both of the short ends of your rectangle to help you seal it. 

Scatter the nuts and chopped chocolate over the dough and lightly press them in with your hands. 

Starting with a short end, roll tightly into a log, sealing the seam and ends. Use a  sharp bread knife to cut the log in half lengthwise (not crosswise) to make two pieces of dough about 10" long each; cut carefully, to prevent too much filling from spilling out. With the exposed filling side up, twist the two pieces into a braid, tucking the ends underneath the loaf, into the prepared bread pan.

Brush the loaf with the egg glaze. Mix together the topping ingredients until crumbly, and sprinkle over the top

Tent with plastic wrap, and let the loaf rise until it is very puffy and has crowned a good inch over the rim of the pan, 1 1/2 to 2 1/2 hours. Towards the end of the rising time, preheat your oven to 325. Alternatively you can let the Babka rise over night in the fridge and bake in the morning. Just pull the loaf out while you are preheating the oven. 

Bake the bread for 35 minutes. Tent lightly with foil at this point if the crumb is getting too dark and bake for an additional 15 to 25 minutes (for a total of 50 to 60 minutes); the babka should be a deep-golden brown. The best way to tell when it is done is to stick an instant read thermometer in the middle, it should read 190. 

Remove from the oven, and immediately loosen the edges with a heatproof spatula. Let the babka cool for 10 minutes, then lift out of the pan with the excess parchment and place onto a rack to cool completely. 

Fight off your family while you let the babka cool so that it is easier to slice, then eventually give in and enjoy a gooey broken piece of this delicious bread.