In a large mixing bowl, combine bread flour, lukewarm water, sourdough starter, and brown sugar. Mix until combined into a shaggy mass. Cover and let it rest for 30 minutes.

Add salt and melted butter to the dough and knead for 8-10 minutes until smooth and elastic.

Place the dough in a lightly oiled bowl and let it ferment at room temperature for 4-6 hours until doubled in size.

Turn the dough onto a floured surface and roll it into a rectangle about 12x18 inches.

Mix brown sugar and cinnamon, brush the dough with melted butter, sprinkle the mixture over the dough, roll it up tightly, and seal the edges.

Slice the rolled log into 1.5-2 inch pieces and arrange them cut-side up in a greased baking pan.

Cover the pan and let the rolls proof for 1.5 to 2 hours, then preheat the oven to 375°F.

Bake for 25-30 minutes until golden brown and fragrant.

Whisk together powdered sugar, milk, and vanilla extract until smooth.

Drizzle icing over the warm focaccia, slice, and serve.