To begin, in a small bowl, combine the warm milk with the active dry yeast and let it sit for 5-10 minutes until frothy. In a large bowl, whisk together the flour, sugar, and salt. Add the melted butter and yeast mixture to the dry ingredients, mixing until a dough forms. Knead the dough for 5 minutes until smooth. Cover and let it rise in a warm place for 1-2 hours, or until doubled in size.

While the dough is rising, prepare the butter for laminating. Place the cold butter between two sheets of parchment paper and use a rolling pin to flatten it into a 6x6 inch square. Refrigerate the butter block to keep it firm until needed.

Once the dough has risen, punch it down and roll it out into a 10x10 inch square on a floured surface. Place the cold butter square in the centre of the dough. Fold the corners of the dough over the butter like an envelope, ensuring the butter is fully enclosed.

Roll out the dough and butter package into a long rectangle, about 8x20 inches. Fold the dough into thirds, like a letter, and rotate it 90 degrees. Wrap it in plastic wrap and refrigerate for 30 minutes to allow the butter to firm up again.

After chilling, roll out the dough again into another long rectangle, fold it into thirds, and refrigerate for another 30 minutes. Repeat this rolling and folding process two more times, ensuring you chill the dough between each step. This process creates the signature flaky layers of the croissant.

Once the folding is complete, roll the dough out into a 10x16 inch rectangle. Cut the dough into 4 equal-sized triangles. Starting from the wide end of each triangle, roll the dough tightly towards the tip to form the classic croissant shape. Tuck the tip under each croissant to maintain the shape while baking.

Place the shaped croissants on a parchment-lined baking sheet. Cover them lightly with a kitchen towel and allow them to rise for 1-2 hours, or until they have nearly doubled in size. Preheat your oven to 400°F (200°C) during the last 30 minutes of rising.

Before baking, lightly brush the croissants with a beaten egg to give them a glossy finish. Bake the croissants for 15-20 minutes, or until golden brown and puffed. Let them cool slightly before serving.