01 - Combine flour, sugar, salt, and yeast in a large bowl, positioning yeast away from direct salt contact. Pour in lukewarm milk, melted butter, and egg. Mix thoroughly until a sticky, uniform dough forms.
02 - Knead dough on a lightly floured surface for 7 to 10 minutes until smooth and elastic. Transfer to a greased bowl, cover, and let rise for 1 hour until doubled in volume.
03 - Punch down risen dough and shape into a rectangle. Wrap and refrigerate for 30 minutes to firm.
04 - On a floured surface, roll dough into a 12 x 16-inch rectangle. Arrange cold butter slices over two-thirds of the dough surface, leaving a 1-inch border.
05 - Fold the unbuttered third over the center, then fold the remaining third over to create a neat rectangular package. Rotate 90 degrees so the open edges face you.
06 - Roll dough again into a 12 x 16-inch rectangle. Perform a letter fold by folding into thirds. Wrap and refrigerate for 30 minutes.
07 - Repeat rolling, folding, and chilling two additional times for a total of three complete turns. Chill 30 minutes between each turn.
08 - After final chill, roll dough to approximately 8 x 16 inches. Roll tightly from the short end into a cylinder, sealing the seam firmly.
09 - Place seam-side down in a greased 9 x 5-inch loaf pan. Cover loosely and let rise until doubled, about 1 hour.
10 - Preheat oven to 375°F. Whisk egg with milk for egg wash. Brush entire loaf surface evenly for golden browning.
11 - Bake for 35 to 40 minutes until deep golden brown and loaf sounds hollow when tapped. Tent with foil if top browns too quickly.
12 - Let cool in pan for 10 minutes, then transfer to wire rack. Cool fully before slicing to maintain texture.