Dissolve yeast in warm water.
Sift 3 cups of the flour into a large mixing bowl, make a deep well and pour in the yeast, milk, sugar, salt, eggs and butter.
Mix until combined. (This can be done using a strong stand mixer such as a Kitchenaid with the dough hook)
Mix in enough of the reserved flour to make a soft dough.
This is then kneaded on a lightly floured board or using the dough hook of your mixer until soft and elastic.
Coat the dough with a little melted butter and return to the bowl to rise, covered until doubled in volume.
Punch down, and allow to rise back to its original size again.
Heat milk and brown sugar to a boil, using a whisk, then add butter and honey and stir till mixed.
Add the ground walnuts, cinnamon, vanilla and cocoa, mix well, then set aside to cool.
When cool, stir in the lightly beaten egg yolks.
Just before spreading the filling on the dough, beat the egg whites till stiff with a pinch of salt and fold into the filling mixture.
Divide the dough in half and roll each piece out on a lightly floured board until quite thin (approx 1/16" / 2mm thick) to give a sheet approximately 14" x 24" (36cm x 61cm)
Spread the filling thinly and evenly over the dough, right to the edges.
Roll the dough to give a 14" (36 cm) roll.
Place in a greased bundt pan, bringing the ends together to form a ring.
Allow each loaf to rise before baking at 325°F or 160°C for about 55 minutes.
Cool slightly before removing from the pan and cooling on a rack.