Activate the Yeast
In a small bowl, combine warm milk, sugar, and yeast.
Let sit for 5–10 minutes until frothy.
Make the Dough
In a large mixing bowl, add flour, salt, softened butter, and yeast mixture.
Knead 8–10 minutes until smooth and elastic.
Cover and let rise in a warm spot for 1 hour, or until doubled.
Prepare the Butter Block
Place cold butter slabs on parchment, shape into a rectangle, and roll slightly flat.
Chill until firm but pliable.
Laminate the Dough
Roll dough into a large rectangle. Place butter block in the center, fold dough over, and seal edges.
Roll out gently, fold into thirds (like a letter). Chill 30 minutes.
Repeat rolling + folding 3 more times, chilling between turns.
Shape the Loaf
Roll dough into a rectangle, then roll tightly like a jelly roll.
Place seam-side down in a greased loaf pan.
Cover and let rise 45 minutes.
Bake
Preheat oven to 375°F (190°C).
Brush with egg wash. Bake 30–35 minutes, until golden brown.
Cool at least 20 minutes before slicing.