In a large mixing bowl, combine the warm water and sourdough starter. Stir in 2 cups of bread flour until you have a shaggy mixture. Let it rest for 30 minutes to an hour.

After resting, mix in the salt and the remaining flour, one cup at a time. Knead until the dough is smooth and elastic, about 10 minutes.

Place the dough in a lightly greased bowl and cover it with a damp cloth. Let it rise for 4-6 hours at room temperature until it's doubled in size.

In a separate bowl, mix together the cinnamon and sugar until well blended.

Once 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. Brush with melted butter, then sprinkle the cinnamon-sugar filling evenly over the dough.

Starting from one long side, carefully roll the dough into a log shape. Pinch the ends to seal, then place it seam-side down into a greased loaf pan.

Cover the loaf with a cloth and let it rise again for about 1-2 hours, until it puffs up slightly over the edges of the pan.

Preheat your oven to 375°F (190°C).

Once the dough has risen, bake for 30-35 minutes or until the top is golden brown and sounds hollow when tapped.

Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely. Slice, serve, and prepare for compliments!