Make the dough

• Mix the sourdough starter, milk, egg, sugar and salt in a bowl.
• Add the bread flour and knead into a soft dough, then work in the softened butter until smooth.
• Cover and let rise until doubled in size.

Mix the cinnamon sugar

• Combine the brown sugar and ground cinnamon in a small bowl.

Roll out and fill

• Roll the dough into a large rectangle on a floured surface.
• Brush generously with melted butter and sprinkle the cinnamon sugar evenly over the top.
• Cut the rectangle into strips, stack them and cut into squares.

Assemble the loaf

• Butter a loaf pan and stack the squares in it, slightly overlapping.
• Cover and let proof until puffy.

Bake

• Bake at 180 °C until deep golden and cooked through.
• Let cool slightly in the pan.

Glaze and serve

• Whisk the powdered sugar with the milk into a smooth glaze.
• Drizzle over the warm bread and pull apart to serve.