Prepare the Croissant Dough:

1. Mix dry ingredients: In a large bowl, combine flour, salt, and sugar.
2. Activate yeast: Dissolve yeast in warm milk and let sit for 5 minutes until foamy.
3. Make dough: Add yeast mixture to flour mixture and knead until smooth (about 5 minutes).
4. First rise: Place in oiled bowl, cover, and let rise for 1 hour.
5. Chill: Refrigerate dough for at least 2 hours or overnight.

Prepare Butter Block:

1. Shape butter: Pound cold butter into a 6×6 inch square between parchment paper.
2. Chill: Keep refrigerated until ready to use.

Make Brownie Batter:

1. Mix wet ingredients: Whisk together melted butter, sugar, eggs, and vanilla.
2. Add dry ingredients: Sift in cocoa powder, flour, and salt. Mix until just combined.
3. Fold in chips: Gently fold in chocolate chips.
4. Chill: Refrigerate while working with dough.

Laminate the Dough:

1. Roll dough: On floured surface, roll chilled dough into 12×8 inch rectangle.
2. Add butter: Place butter block on one half of dough, fold other half over.
3. First fold: Roll out to 18×8 inches, fold into thirds like a letter.
4. Chill: Wrap and refrigerate 30 minutes.
5. Second fold: Repeat rolling and folding process.
6. Final chill: Refrigerate for another 30 minutes.

Assemble Croissants:

1. Roll out: Roll dough into 16×12 inch rectangle.
2. Cut triangles: Cut into 8 triangles (4×3 inch base).
3. Add filling: Place 1-2 tablespoons brownie batter at wide end of each triangle.
4. Roll up: Roll from wide end to point, sealing edges.
5. Shape: Place on parchment-lined baking sheets, curve into crescent shape.

Final Rise and Bake:

1. Rise: Cover and let rise in warm place for 45 minutes.
2. Preheat: Heat oven to 375°F (190°C).
3. Egg wash: Brush tops with beaten egg.
4. Bake: Bake 15-18 minutes until golden brown and internal temperature reaches 190°F.
5. Cool: Let cool on wire rack for 10 minutes.