Place the flour in a large bowl. Put the salt on one side and the sugar on the other. Make a well in the center and crumble in the fresh yeast. Add the milk and water, then mix with a dough hook or knead by hand until the dough no longer sticks to the sides of the bowl. Cover with plastic wrap and let rise for about 1 hour, until the dough doubles in size.

Punch down the dough and shape it into a rectangle. Cover with plastic wrap and let rest in the refrigerator for 2 hours.

Take the butter and wrap it in parchment paper to form a 8x8 inch (20x20 cm) square. Pound it with a rolling pin, then roll it out to about 1/2 inch (1 cm) thick. Place in the refrigerator.

Roll out the dough into a 8x16 inch (20x40 cm) rectangle. Place the butter on top, then fold the dough over to enclose the butter. Press down gently with your rolling pin.

Roll the dough out again into a rectangle. Fold the bottom and top edges toward the center, then fold in half to create a double turn (book fold). Wrap in plastic wrap and let rest for 30 minutes in the refrigerator.

Melt the chocolate. Cover a board with plastic wrap and spread the melted chocolate on it. Place in the refrigerator.

Roll out the dough to 16 to 20 inches (40 to 50 cm) wide. Cut it in half, then cut strips about 4 inches (10 cm) high.

Cut the chocolate into bars and place one bar about 1 1/2 inches (4 cm) from the edge of each strip. Place a second bar, then roll up the dough to enclose the chocolate.

Place the rolls in the oven (turned off) for 20 to 30 minutes with a pan of boiling water underneath to proof. Open the oven occasionally to let out steam.