01 - In a large bowl, combine flour, sugar, salt, and yeast, ensuring yeast does not directly contact salt. Add lukewarm milk, melted butter, and egg. Mix until a sticky dough forms.
02 - Knead the dough for 7 to 10 minutes until smooth and elastic. Transfer to a greased bowl, cover, and let rise for 1 hour or until doubled in size.
03 - Punch down the dough and shape into a rectangle. Cover and refrigerate for 30 minutes to firm.
04 - On a 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 section, then fold the remaining third on top to create a neat rectangle. Rotate 90 degrees so the open edges face you.
06 - Roll the dough into a 12 x 16-inch rectangle again. Perform a letter fold by folding into thirds. Wrap tightly and refrigerate for 30 minutes.
07 - Repeat the rolling, folding, and chilling process two additional times for a total of three complete turns, chilling 30 minutes between each.
08 - After the final chill, roll dough to approximately 8 x 16 inches. Roll tightly from the short edge into a log shape, sealing the seam.
09 - Place the loaf seam-side down in a greased 9 x 5-inch loaf pan. Cover loosely and let rise until doubled in size, about 1 hour.
10 - Preheat oven to 375°F. Whisk together egg and milk until smooth for the egg wash.
11 - Brush the loaf surface with egg wash. Bake for 35 to 40 minutes until golden brown and hollow when tapped. Tent with foil if browning too quickly.
12 - Allow the bread to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.