Dissolve yeast in the warn water in a large bowl. Add the milk, eggs, butter, sugar, salt and 3 cups flour. Beat on medium speed until smooth. Stir in only enough remaining flour to form a soft dough. It is possible you will need more flour so you can add about 1/2 cup. I used 6 cups of flour in the loaves in the pics. The amount of flour can vary so always go by the consistency of the dough.
Turn dough out on a floured surface and knead until smooth and elastic; about 8 minutes. Alternatively, if you have a heavy stand mixer, switch to the dough hook and let the machine do the work.
Place dough in a greased bowl turning once so the top of the dough is greased. Cover and let rise in a warm, draft-free place for 1 1/2 to 2 hours.
Punch dough down and turn onto a lightly floured surface and divide into 6 equal portions. Roll each portion into a 14-inch/36 cm rope.
For each loaf, braid 3 ropes together on a parchment lined baking sheet. Cover with a kitchen towel (no plastic here) and let rise until doubled; about 50 minutes.
Preheat oven to 375F/190C.
Beat egg yolk and 2 tbs water. Brush over loaves and sprinkle with sesame seeds.
Bake for 30-35 minutes until golden brown. Remove to wire racks to cool completely.