1. **Mix the Dough**: In the bowl of a stand mixer fitted with the dough hook, combine the strong bread flour, all-purpose flour, granulated sugar, salt, and instant dry yeast. Mix briefly to combine.

2. **Add Liquids**: Pour in the cold milk and cold water. Mix on low speed for 3-4 minutes until a shaggy dough forms and all flour is hydrated. Increase speed to medium-low and knead for another 5-7 minutes until the dough is smooth, elastic, and pulls away from the sides of the bowl. It will still be slightly sticky.

3. **First Chill**: Form the dough into a rectangular shape, wrap tightly in plastic wrap, and refrigerate for at least 1 hour, or preferably overnight (up to 12 hours). This chill helps relax the gluten and makes it easier to work with.

4. **Prepare the Butter Block**: Cut the cold butter into 1 cm thick slices. Arrange them close together between two large sheets of parchment paper (about 30x20 cm / 12x8 inches). Using a rolling pin, pound the butter until it forms a uniform rectangle, about 20x15 cm (8x6 inches) and about 5 mm thick. Make sure the butter is pliable but still cold. Refrigerate the butter block while you prepare the dough for lamination.

1. **First Turn (Single Fold)**: On a lightly floured surface, roll out the chilled dough into a rectangle about 40x20 cm (16x8 inches). It should be twice as long as your butter block.

2. **Encase the Butter**: Place the cold butter block in the center of the dough. Fold one side of the dough over the butter, then fold the other side over, enclosing the butter completely. Pinch the seams to seal the butter inside. You should now have a dough packet roughly 20x15 cm (8x6 inches).

3. **First Roll**: Rotate the dough 90 degrees so the seam is facing your left or right. Gently and evenly roll the dough into a rectangle about 60x20 cm (24x8 inches), maintaining an even thickness.

4. **First Fold (Letter Fold)**: Brush off any excess flour. Fold one-third of the dough over towards the center, then fold the remaining one-third over the top, like folding a letter. This is a "single fold" or "letter fold." You should have three layers of dough and two layers of butter.

5. **First Chill**: Wrap the folded dough tightly in plastic wrap and refrigerate for at least 30 minutes (or up to 1 hour) to allow the butter to firm up and the gluten to relax.

6. **Second Turn (Single Fold)**: Repeat the rolling and folding process. Take the dough out of the fridge, rotate it 90 degrees (seam to the side), and roll it out again to about 60x20 cm (24x8 inches). Perform another single fold.

7. **Second Chill**: Wrap and refrigerate for at least 30 minutes.

8. **Third Turn (Single Fold)**: Repeat the rolling and folding process one last time. Take the dough out, rotate 90 degrees, roll to 60x20 cm, and perform a final single fold.

9. **Final Chill**: Wrap the dough tightly and refrigerate for a minimum of 2 hours, or preferably overnight (10-12 hours). This extended chill is crucial for flavor development and ease of shaping.

1. **Prepare for Shaping**: Remove the dough from the refrigerator. On a lightly floured surface, roll the dough into a large rectangle, about 70x30 cm (28x12 inches) and 3-4 mm thick. Work quickly but gently to keep the butter cold.

2. **Trim and Cut**: Trim the edges to create clean lines. Cut the dough into two equal strips lengthwise (about 70x15 cm / 28x6 inches each). Then, cut each strip into triangles. For classic croissants, cut isosceles triangles with a base of about 8-10 cm (3-4 inches) and a height of 15-20 cm (6-8 inches). You should get 6-8 triangles per strip, totaling 12-16 croissants.

3. **Shape the Croissants**: Make a small slit (about 1.5 cm / 0.5 inch) in the center of the base of each triangle. Gently stretch the base of the triangle outwards slightly, then roll tightly from the base towards the tip, pulling gently as you roll to create tension. Curve the ends inward slightly to form the classic crescent shape.

4. **Proofing**: Arrange the shaped croissants on baking sheets lined with parchment paper, leaving ample space between them. Cover loosely with plastic wrap or a large, clean kitchen towel. Let them proof in a warm, draft-free place for 2-3 hours, or until they are visibly puffy, jiggly, and nearly doubled in size. They should feel very light. The layers should be distinct but not splitting.

5. **Preheat Oven**: About 30 minutes before baking, preheat your oven to 190°C (375°F).

6. **Prepare Egg Wash**: Whisk together the egg and milk for the egg wash.

7. **Egg Wash and Bake**: Gently brush the tops of the proofed croissants with the egg wash, being careful not to let it drip down the sides (this can hinder rising).

8. **Bake** for 15-20 minutes, or until deep golden brown and well-risen. Rotate the baking sheets halfway through for even baking.

9. **Cool**: Transfer the baked croissants to a wire rack to cool slightly before serving.