Put the flour in a large bowl, mix with salt, sugar, add the butter in flakes.

Dissolve the yeast in the milk. Add the liquid to the flour.

Beat the egg, add about half of it to the flour, set aside the rest.

Knead until you obtain a smooth, even dough. Cover and let stand in a warm place until double in size (about 1h).

Separate the dough in half and roll it into 2 equal strands, keep the strands slightly thicker in the middle.

Braid the strands. I found a sketch here, it's not as difficult as it looks: http://www.instructables.com/image/FV25C5AF6B7T1NX. Put the Zopf on a baking tray.

Here is an alternative way to braid for the super lazy: put the two strands side by side and simply twist them into each other. Then fold the resulting single, twisted strand in the middle and again twist the two ends into each other.

Brush the Zopf with the remaining egg. Let stand for another 15 to 20 minutes.

Put into the cold oven, set the temperature to 220C. Bake for 35 to 45 minutes. If you knock on the underside of the finished Zopf, it should sound hollow.