Pour room-temperature milk and water in a bowl; combine the yeast in;Just warm up a little bit if you use cold milk but do not overheat as it would neutralize the yeast action;
In a small bowl, crack and whisk the egg;
In a food processor fitted with a knead head, tip the flour and make a well; pour the milk and water with yeast; knead at low speed; add the egg;You can knead by hand if you prefer.
Add the vegetable charcoal powder and continue to knead;
Knead until the dough is set; it may be a little bit sticky at this point;
With extra flour, dust a clean working area and finish to knead by hands until the dough forms a non-sticky ball; pressing with a fingertip should mark the dough without spring back;
Place the dough into a deep bowl;Soaked a clean kitchen cloth with hot water; wring water out well.Cover the dough with it and leave the dough to rise for 1 hour at room temperature;
Take the ball and cut into 4 even parts; shape a bowl with each part; place on a flour-dusted tray; leave space between buns;
Cover with a kitchen cloth and leave to rise for 1 hour;
Preheat the oven to 180C / gas 6;
With a spoon, mix one egg yolk with 2 teaspoons of water; brush buns with the egg and sprinkle the seeds over the buns;Place on a baking tray;
Bake for 15-20 minutes;
Remove buns from the oven and leave to cool down under a dry kitchen cloth.Enjoy!