Classic French laminated pastry, built by folding a block of cold butter into yeasted dough through three single folds to create dozens of paper-thin layers - keeping the butter and dough at the same cool, pliable temperature throughout is what lets the layers stay distinct instead of the butter melting into the dough or cracking apart under the rolling pin.
1.Dissolve the yeast and sugar in the cold milk and let sit for 5 minutes.
2.Mix the flour and salt in a large bowl, add the yeast mixture and the 2 tbsp softened butter, and knead for 6-8 minutes into a smooth, slightly firm dough. Wrap and refrigerate for at least 1 hour.
3.Meanwhile, pound the cold butter between two sheets of parchment into a flat 8x8-inch square, then chill it - it needs to stay cold but flexible enough to bend without cracking, the same consistency as the chilled dough.
4.Roll the dough into a rectangle roughly twice the size of the butter block. Place the butter block in the center and fold the dough over it to fully enclose it, pinching the seams shut.
5.Roll the dough-wrapped butter out into a long rectangle, then fold it in thirds like a letter - this is the first single fold. Wrap and chill for 30-45 minutes.
6.Repeat the roll-and-fold two more times, chilling for 30-45 minutes between each fold - keeping the butter and dough at the same cool, pliable temperature throughout these folds is what keeps the layers distinct instead of the butter melting into the dough or cracking apart.
7.After the final fold and chill, roll the dough out into a large rectangle about 1/4 inch thick. Cut into triangles, then roll each triangle up from the wide end to the point to shape the croissants.
8.Place on a baking sheet, cover loosely, and let rise in a warm spot for 1.5-2 hours, until visibly puffy and jiggly.
9.Preheat the oven to 400°F. Brush the croissants with the egg wash and bake for 15-18 minutes, until deep golden brown and the layers are visible on the ends.