1. Prepare the Dough

1. In a mixing bowl, combine sourdough starter, warm milk, and sugar. Stir to dissolve.
2. Add bread flour and salt, mixing until a shaggy dough forms.
3. Knead with a stand mixer (or by hand) for 5-7 minutes, until smooth.
4. Add softened butter, one tablespoon at a time, kneading until fully incorporated.
5. Cover and ferment at room temperature for 4-6 hours, until doubled.

2. Chill the Dough

1. After fermentation, shape the dough into a rectangle and refrigerate for at least 1 hour.

3. Prepare the Butter Block

1. Place cold butter between two sheets of parchment paper.
2. Roll into a 7×10-inch rectangle, then refrigerate until firm.

4. Laminate the Dough (Layering the Butter)

1. Roll the chilled dough into a 10×14-inch rectangle.
2. Place the butter block in the center, folding the dough over like a letter.
3. Roll out to 10×14 inches again, then fold into thirds.
4. Repeat this rolling and folding process twice more, chilling for 30 minutes between folds.

5. Shape & Proof the Bread

1. Roll out the laminated dough into a 10×14-inch rectangle.
2. Cut into three equal strips, then stack the strips together.
3. Twist and place in a buttered loaf pan.
4. Cover and proof at room temperature for 6-8 hours (or overnight in the fridge) until puffy.

6. Bake Until Golden

1. Preheat oven to 375°F (190°C).
2. Brush with egg wash.
3. Bake for 35-40 minutes, until deep golden brown.
4. Let cool for 15 minutes before slicing.