1. In a large bowl, combine the flour, sugar, and salt.
2. Dissolve the yeast in the warm milk and let it sit for about 5 minutes.
3. Add the yeast mixture to the flour mixture and mix until combined.
4. Add the cold butter pieces and mix until the dough is crumbly.
5. Roll out the dough on a floured surface into a large rectangle.
6. Fold the dough into thirds, like a letter, and roll it out again. Repeat this process 3 times.
7. Cut the dough into triangles and place a few chocolate chips at the base of each triangle.
8. Roll up the triangles from the base to the tip to form croissants.
9. Place the croissants on a baking sheet lined with parchment paper and let them rise for about 30 minutes.
10. Preheat the oven to 375°F (190°C).
11. Brush the croissants with the beaten egg.
12. Bake for 15-20 minutes or until golden brown.