In a stand mixer, combine 4 cups of all-purpose flour, 1/4 cup of granulated sugar, 1 tablespoon of salt, and 2 1/4 teaspoons of instant yeast. Gradually mix in 1 1/2 cups of cold whole milk until a soft dough forms. Knead on medium speed for about 5 minutes until smooth. Cover the bowl with plastic wrap and refrigerate the dough for 30 minutes to chill.

While the dough rests, take 1 cup of unsalted butter, softened, and mix it with 1/4 cup of all-purpose flour until well combined. Shape the mixture into a flat rectangle, roughly 8x6 inches, and wrap it in parchment paper. Chill the butter layer in the refrigerator for 30 minutes until it's firm but pliable.

On a lightly floured surface, roll the chilled dough into a rectangle, approximately 20x10 inches. Place the chilled butter layer in the center, folding the dough over to encase it. Seal the edges and roll it out gently to a 24x10 inch rectangle. Fold the dough into thirds like a letter, cover it, and refrigerate for 30 minutes. Repeat this process two more times, rolling and folding, then refrigerate for an additional 4 hours or overnight.

After the final chill, roll out the dough into a large rectangle, about 24x12 inches. Cut the dough into triangles, roughly 4 inches wide at the base.

Place a piece of chocolate baton at the wide end of each triangle, then roll the dough tightly toward the tip. Position the formed croissants on lined baking sheets, curving them slightly into a crescent shape.

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

Preheat your oven to 400°F (204°C). In a small bowl, whisk together 1 egg and 1 tablespoon of milk to create an egg wash. Brush the croissants generously with the egg wash to promote a beautiful golden-brown finish.

Bake for 20 minutes, rotating the baking sheets halfway through, until the croissants are puffed and deeply golden.

Let them cool slightly on a wire rack and dust with confectioners' sugar before serving, if desired.