**Make the Détrempe (Dough Base):**
- Combine the bread flour, all-purpose flour, yeast, sugar, and salt in a large bowl.
- Gradually add the warm water and milk. Mix until the dough forms a smooth, slightly puffy texture.
- Knead for about 10 minutes to develop the dough’s gluten. Let it rise at room temperature for 45-60 minutes, then refrigerate for 4-12 hours.
**Prepare the Butter Block (Tourrage):**
- Cut cold European-style butter into 1-inch pieces. Mix it with a small amount of flour to create a smooth, pliable butter block.
- Form the butter into a 8-inch square about 1/2 inch thick. Refrigerate for 30 minutes to keep the butter firm but soft.
**Lamination Process:**
- Roll the chilled détrempe into a large rectangle. Place the butter block on top and fold the dough around the butter.
- Perform a letter fold to encase the butter, then chill the dough for 30 minutes. Repeat the folding process for two additional turns.
- Refrigerate for 1 hour after the final turn to allow the dough to firm up.
**Shaping the Croissants:**
- Roll the dough into a 13" x 18" rectangle and trim the edges for neatness.
- Cut the dough into triangles and make a small 1-inch notch at the wide end of each triangle.
- Roll the triangles tightly from the wide end to the tip to form croissants. Place on a baking sheet.
**Proofing:**
- Allow the shaped croissants to proof in a warm, humid environment for about 2-2.5 hours or until they double in size. They should feel soft and slightly jiggly when gently pressed.
**Baking the Croissants:**
- Preheat the oven to 425°F. Brush the croissants with an egg wash (1 beaten egg mixed with 1 tablespoon water).
- Bake for 15 minutes at 425°F to create a crisp exterior, then reduce the temperature to 350°F and bake for another 10-15 minutes, or until golden-brown.
**Cool and Serve:**
- Allow the croissants to cool for a few minutes on a wire rack. Enjoy them fresh with butter or jam for the ultimate indulgence.