# Directions:
01 - In a large bowl, combine bread flour, granulated sugar, and fine sea salt. Add cold milk, sourdough starter, and softened butter. Mix until just incorporated. Knead until a smooth, elastic dough forms, approximately 8 minutes.
02 - Shape dough into a rectangle, wrap in plastic wrap, and refrigerate for at least 2 hours.
03 - Place cold butter between two sheets of parchment paper. Pound and roll into a 8 x 6 inch rectangle. Chill until firm but still pliable.
04 - On a lightly floured surface, roll dough to a 16 x 8 inch rectangle. Position butter block on one half of dough, fold dough over to cover, and seal edges firmly.
05 - Turn dough 90 degrees and roll into a 24 x 8 inch rectangle. Fold into thirds in letter-fold style, wrap in plastic, and refrigerate for 1 hour.
06 - Repeat rolling and folding process two additional times, refrigerating for 1 hour between each turn.
07 - After final fold, wrap dough and refrigerate overnight, 8 to 12 hours.
08 - The following morning, roll dough to a 24 x 12 inch rectangle, approximately 1/5 inch thick. Cut into 12 long triangles using a sharp knife or pastry cutter.
09 - Starting from the wide end of each triangle, tightly roll toward the point, tucking the tip underneath to form a crescent shape. Arrange on parchment-lined baking sheets.
10 - Cover loosely and proof at room temperature until doubled in size, approximately 2 to 3 hours.
11 - Preheat oven to 400°F (200°C).
12 - Whisk together egg and milk. Brush croissants lightly with egg wash mixture.
13 - Bake for 18 to 22 minutes until golden brown and crisp. Cool briefly before serving.