01 - Combine flour, sugar, salt, and yeast in a large bowl, keeping yeast away from direct salt contact. Pour in lukewarm milk, melted butter, and egg. Mix until a sticky, shaggy dough forms.
02 - Knead dough on a floured surface for 7 to 10 minutes until smooth and elastic. Transfer to a greased bowl, cover, and let rise in a warm place 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 lightly floured surface, roll dough into a 12 x 16-inch rectangle. Arrange cold butter slices over two-thirds of the dough, leaving a 1-inch border.
05 - Fold the unbuttered third over the buttered portion, then fold remaining third on top to create a neat rectangle. Rotate 90 degrees so open ends face you.
06 - Roll dough again into a 12 x 16-inch rectangle. Perform a letter fold into thirds. Wrap and chill for 30 minutes.
07 - Repeat rolling, folding, and chilling two more times for a total of three complete turns. Chill 30 minutes after each turn.
08 - After final chill, roll dough to approximately 8 x 16 inches. Roll tightly from the short edge into a cylinder, sealing the seam.
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 1 tablespoon milk until smooth. Brush entire surface of loaf generously with egg wash.
11 - Bake for 35 to 40 minutes until deep golden brown and loaf sounds hollow when tapped. Tent loosely with foil if top browns too quickly.
12 - Let loaf rest in pan for 10 minutes, then transfer to wire rack. Cool completely before slicing for clean, even cuts.