Whisk flour, sugar, salt, and yeast in a large bowl. Add cold milk and softened butter. Mix until a shaggy dough forms.
Knead by hand 3–4 minutes just until smooth and cohesive. Do not overwork. The dough should feel cool and slightly firm.
Flatten into a 1-inch-thick rectangle. Wrap and chill 30–45 minutes. Cold dough resists over-stretching and helps lamination.
Place butter between two sheets of parchment. Tap and roll into a 6x8-inch (15x20 cm) rectangle, about 1/2 inch thick.
Square the edges with a bench scraper. Chill 10–15 minutes until cool yet pliable. Butter should bend without cracking or feeling greasy.
On a lightly floured surface, roll dough into a 10x16-inch (25x40 cm) rectangle.
Place the butter block in the center, with the short side parallel to the short side of the dough.
Fold both short ends of dough over the butter to meet in the middle, then pinch the seams. You now have a neat packet.
Roll the packet into an 8x24-inch (20x60 cm) rectangle. Keep edges straight; add flour as needed but brush off excess.
Fold like a letter: bottom third up, top third down over it. That’s one turn.
Wrap and chill 30 minutes. Resting prevents butter from smearing into the dough.
Repeat the rolling to 8x24 inches and do another letter fold. Chill 30 minutes.
Do a third letter fold the same way. Chill at least 1 hour or up to overnight for best flavor.
Roll the laminated dough into a 12x24-inch (30x60 cm) rectangle, about 1/4 inch thick. Trim edges to reveal clean layers.
Cut into 16 rectangles, each 3x6 inches (7.5x15 cm).
Place a chocolate baton along the short edge of one rectangle. Roll the dough over the baton one full turn.
Add a second baton and continue rolling to the end, seam side down. Do not press flat; keep the roll plump.
Arrange on a parchment-lined sheet, leaving space to expand.
Cover loosely and let rise at 75–80°F (24–27°C) for 1.5–2 hours until puffy, jiggly, and about 50% larger. The layers should look distinct.
They should feel airy when gently shaken, not dense. If the butter looks melty, chill 10 minutes and resume proofing in a cooler spot.
Heat oven to 400°F (200°C). Brush pastries lightly with egg wash, avoiding the cut edges.
Bake 18–22 minutes until deep golden brown with a glossy top and crisp bottoms. Rotate pans halfway for even color.
Cool 15 minutes before serving. The chocolate finishes melting as they rest.
