In a stand mixer, combine 4 cups of all-purpose flour, 1/4 cup of granulated sugar, 1 teaspoon of salt, and 2 1/4 teaspoons of instant yeast. Gradually pour in 1 1/4 cups of cold whole milk and knead the mixture with a dough hook for about 5 minutes until the dough is soft yet slightly tacky. Cover and refrigerate for 30 minutes.

Prepare the butter layer by softening 1 cup of unsalted butter and mixing it with 2 tablespoons of all-purpose flour. Shape into a rectangle about 1/2 inch thick, wrap it in parchment paper, and chill for 30 minutes.

Roll out the dough into a rectangle 1/2 inch thick. Place the chilled butter layer in the center, fold the dough over to encase it, seal the edges tightly, and roll the dough out to a larger rectangle. Fold into thirds, wrap in plastic, and refrigerate for 30 minutes.

Remove the dough and roll it out again into a rectangle, fold into thirds, and refrigerate for 30 minutes. Repeat this process one more time.

After the last fold, give the dough a final chill in the refrigerator for at least 4 hours or overnight.

Roll the dough out into a rectangle about 1/4 inch thick. Cut into triangles, place a chocolate piece at the wide end, and roll tightly to form crescents. Place on lined baking sheets with tips tucked underneath.

Cover the arranged croissants and let rise for about 1 hour, or until puffed up. Refrigerate for an additional hour.

Preheat the oven to 400°F (204°C). Whisk together a large egg and 1 tablespoon of milk, brush the tops of the croissants with the egg wash, and bake for 20 minutes until golden brown.

Remove from the oven and cool on a wire rack for about 10 minutes. Dust with confectioners' sugar if desired before serving.