01 - In a large bowl, combine flour, sugar, salt, and yeast, ensuring yeast is placed away from direct salt contact. Pour in lukewarm milk, melted butter, and beaten egg. Mix thoroughly until a sticky, shaggy dough forms.
02 - Knead the dough on a lightly floured surface for 7 to 10 minutes until smooth and elastic. Transfer to a greased bowl, cover with plastic wrap or damp towel, and let rise in a warm area for 1 hour or until doubled in volume.
03 - Punch down the risen dough to release air. Shape into a rough rectangle, wrap in plastic, and refrigerate for 30 minutes to firm the gluten structure.
04 - On a floured surface, roll the chilled 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 of dough over the center buttered portion. Fold the remaining third over to create a neat rectangle. Rotate the dough 90 degrees so the open edges face you.
06 - Roll the dough again into a 12 x 16-inch rectangle. Perform another letter fold by folding into thirds. Wrap tightly and refrigerate for 30 minutes.
07 - Repeat the rolling and folding process two additional times, chilling 30 minutes between each turn, for a total of three complete laminations. Keep dough chilled throughout to prevent butter melting.
08 - After the final chill, roll dough to approximately 8 x 16 inches. Starting from a short edge, roll tightly into a cylinder, sealing the seam firmly.
09 - Place the shaped loaf seam-side down in a greased 9 x 5-inch loaf pan. Cover loosely with plastic and let rise in a warm place until doubled, about 1 hour.
10 - Preheat oven to 375°F. Whisk together egg and milk until smooth. Brush the entire surface of the risen loaf gently with the egg wash mixture.
11 - Bake for 35 to 40 minutes until deeply golden brown and the loaf sounds hollow when tapped on the bottom. Tent with aluminum foil if the surface browns too quickly.
12 - Allow the loaf to rest in the pan for 10 minutes. Transfer to a wire rack and cool completely before slicing to prevent tearing the delicate layers.