Put the flour, sugar, yeast, salt, milk and five eggs into a free-standing food mixer and mix, for about five minutes, to a smooth dough. If mixing by hand, this will take about eight minutes.
Add the butter to the dough and mix for a further five minutes in the mixer, or 10 minutes by hand. Put the dough into a bowl, cover and leave in the fridge overnight.
The dough should now be stiff and easily shaped. Cut the dough into 50g/1¾oz pieces and divide 45g/1½oz for the brioche bodies and 5g/¼oz for the brioche heads.
Using your hands, shape the dough pieces into balls. Put each large piece of dough into a brioche mould and push a smaller dough on top of each once. Leave the brioche in a warm place to rise for one hour.
Preheat the oven to 200C/400F/Gas 6. Brush the brioche with the egg wash and bake for 20 minutes, or until golden-brown.
Transfer to a wire rack to cool.