Mix milk with yeast and sugar and let it rest for 5 minutes.
Put flour and salt in your mixing bowl and add the milk and soft butter.
Insert the dough hook and knead for 10 to 15 minutes, until the dough pulls away from the sides. Let the dough rest for 1 hour with the plastic cover on and closed.
Dust your work surface with some flour. Place the dough on it and shape it into a flat ball. Divide into four and then each piece into 3 equal pieces so you get 12 pieces of equal size. Shape them nicely, flatten them a bit and place them on a greased rectangular baking sheet. These buns will bake close together. You can also place them completely apart on a larger baking sheet if you prefer them to be fully round.
Cover with plastic wrap and let rise for 30 to 60 minutes in a warm place.
Sprinkle with some fleur de sel.
Bake them for about 25 minutes in a preheated oven at 175°C
Brush them one by one immediately with melted butter as they come out of the oven.
Place on the table and top as desired, ideal bun for burgers!