Creating homemade French croissants involves several steps that require attention to detail. Follow these instructions carefully:

1. Mix the Dough: In a large bowl, combine warm milk, warm water, yeast, and sugar. Let it sit for about 5 minutes until it becomes frothy.
2. Add Dry Ingredients: Add flour and salt to the yeast mixture. Mix until a dough forms.
3. Knead the Dough: Lightly flour your work surface and knead the dough for about 5 minutes until it’s smooth.
4. First Chill: Shape the dough into a ball, wrap it in plastic, and chill in the refrigerator for 1 hour.
5. Prepare Butter Block: While the dough chills, shape the cold butter into a rectangle (about 8×6 inches) between parchment paper. Chill again for 30 minutes.
6. Laminate the Dough: Roll out the chilled dough into a rectangle (about 16×10 inches). Place the butter block in the center and fold the dough over it, sealing the edges.
7. First Fold: Roll the dough into a rectangle again, then fold it into thirds like a letter. Wrap and chill for 30 minutes.
8. Repeat the Folds: Roll out the dough again, fold it into thirds, and chill for another 30 minutes. Repeat this process a total of three times.
9. Shape the Croissants: Roll out the dough into a large rectangle, and cut it into triangles. Roll each triangle from the base to the tip to form the croissant shape.
10. Final Rise: Place the shaped croissants on a baking sheet lined with parchment paper. Let them rise in a warm place for about 1 hour until they are puffy.
11. Preheat Oven: Preheat your oven to 400°F (200°C).
12. Egg Wash: Beat the egg and brush it over the croissants for a golden finish.
13. Bake: Place the croissants in the preheated oven and bake for 15-20 minutes until they are golden brown and flaky.
14. Cool: Remove from the oven and let cool on a wire rack for a few minutes before serving.