In a mixing bowl, combine the bread flour and salt. In a separate bowl, mix the water and sourdough starter until well combined. Pour the wet ingredients into the dry ingredients and mix until a shaggy dough forms.

Knead the dough on a floured surface for about 10 minutes until smooth and elastic. Place the dough in a lightly greased bowl, cover with a kitchen towel, and let it rise at room temperature for 3-4 hours or until doubled in size.

In a small bowl, mix the brown sugar and ground cinnamon together. Set aside.

After the dough has risen, punch it down and turn it out onto a floured surface. Roll it into a rectangle about 1/2 inch thick.

Spread the softened butter over the dough, then sprinkle the cinnamon-sugar mixture evenly on top, followed by the soaked raisins.

Starting from one long edge, roll the dough tightly into a log. Pinch the seams to seal. Place the log seam-side down in a greased loaf pan.

Cover the loaf with a kitchen towel and let it rise for another 1-2 hours until puffy.

Preheat the oven to 375°F (190°C). Bake the loaf for 40-45 minutes until golden brown and hollow sounding when tapped. Let cool before slicing.