In a stand mixer, combine flour, sugar, salt, and yeast. Gradually add cold milk, kneading for about 5 minutes. Refrigerate for 30 minutes.

Beat softened butter with flour until smooth, shape into a rectangle, wrap in parchment, and chill for 30 minutes.

Roll out chilled dough into a 10x20 inch rectangle, enclose chilled butter inside, pinch edges, and roll into a longer rectangle. Refrigerate for 30 minutes.

Repeat rolling and folding two more times for a total of three folds, refrigerating for 30 minutes each time.

Wrap the dough tightly in plastic and refrigerate for at least 4 hours, or overnight.

Roll the dough into a 10x30 inch rectangle, cut into 4x6 inch rectangles, fill with chocolate batons, roll up, and shape into croissants.

Proof croissants at room temperature for 1 hour, then refrigerate for another hour.

Preheat oven to 400°F. Brush croissants with egg wash and bake for 20 minutes until puffed and golden.

Cool on a wire rack for a few minutes, dust with confectioners’ sugar, and serve.