In a large mixing bowl, combine the sourdough starter and warm water. Stir until well mixed.

Add the dark brown sugar and molasses, then mix until fully combined.

In a separate bowl, mix the flour, spices, salt, and baking soda.

Gradually add the dry ingredients to the wet mixture, stirring until a soft dough forms.

Knead the dough on a floured surface for about 5-10 minutes, until it becomes smooth and elastic.

Place the kneaded dough in a greased bowl, cover it with a cloth, and let it rise in a warm place for 4-6 hours or until it doubles in size.

Once risen, punch down the dough and shape it into a loaf. Place it in a greased loaf pan.

Let it rise again for an additional 1-2 hours.

Preheat your oven to 375°F (190°C).

Bake the bread for 30-35 minutes or until golden brown. A toothpick inserted into the center should come out clean.

Once baked, let it cool on a wire rack before slicing.