In a large mixing bowl, combine all-purpose flour, granulated sugar, and salt. In a separate bowl, dissolve active dry yeast in warm milk and let it foam for about 5 minutes. Pour this mixture along with melted unsalted butter into the flour mixture and knead until the dough is smooth, roughly 10 minutes. Cover with plastic wrap and refrigerate for 1 hour to allow it to relax.

While the dough chills, prepare the butter block. Take cold unsalted butter and place it between two sheets of parchment paper. Using a rolling pin, flatten the butter into a 6-inch square. Ensure it is even and smooth. Wrap the butter in the parchment paper and freeze it for about 30 minutes until it’s firm yet pliable for layering.

After chilling the dough and butter, roll the dough out on a lightly floured surface into a 12-inch square. Place the butter block in the center and fold the corners of the dough over the butter to completely enclose it. Pinch the edges to seal.

Now, carefully roll the enclosed dough into a rectangle, approximately 8 by 20 inches. Once rolled out, fold the rectangle into thirds like a letter, then wrap it and chill in the refrigerator for 30 minutes. Repeat this turning process two more times, with resting periods in between.

Once the turns are complete and the final dough is chilled, roll it out to a thickness of 1/4 inch. Cut triangles with a 5-inch wide base. Starting from the wide end, roll each triangle tightly towards the tip, forming a crescent shape.

Place the shaped croissants on a lined baking sheet, cover them with a clean kitchen towel and let them rise at room temperature for 1.5 to 2 hours, or until they appear slightly puffy and almost doubled in size.

Preheat your oven to 400°F (200°C). In a small bowl, whisk together an egg and a splash of milk for the egg wash, then brush the croissants lightly with the mixture. Bake in the preheated oven for 18-22 minutes, or until they are golden brown and flaky.