In a mixing bowl, combine active sourdough starter, lukewarm milk, egg, sugar, salt, and instant yeast.

Gradually add all-purpose flour and 10 tablespoons of softened butter, mixing until a shaggy dough forms.

Knead the dough for 6-8 minutes until smooth and elastic.

Shape the dough into a ball, place in greased bowl, cover with a kitchen towel, and let rise at room temperature for 3-4 hours.

Place 8 tablespoons of cold butter between parchment paper and shape into a 7x7-inch square.

Chill in the refrigerator for 20-30 minutes.

After the first rise, roll the dough into a 10x10 inch square.

Place the chilled butter block in the center and fold corners over to encase the butter.

Roll into a 10x20 inch rectangle, fold into thirds like a letter and refrigerate for 30 minutes.

Roll the lamination dough into a 12x20 inch rectangle.

Sprinkle chocolate chips, fold and roll the dough to encase completely.

Shape into a loaf and place in a greased loaf pan.

Cover the loaf and let rise for about 2 hours in a warm spot.

Preheat the oven to 375°F (190°C) about 20 minutes before baking.

Bake for 30-35 minutes until golden brown and hollow when tapped.

Allow the loaf to cool in the pan for 10 minutes, then transfer to a wire rack for at least 1 hour.