In the large mixing bowl, combine the all-purpose flour, whole wheat flour, and salt.
Mix the active sourdough starter with the lukewarm water until well incorporated.
Gradually add the wet mixture to the dry ingredients while stirring until a shaggy dough forms.
Knead the dough for about 10 minutes until it becomes smooth and elastic.
Place the dough back into the bowl, cover it with a clean cloth or plastic wrap, and let it rest at room temperature for 4-6 hours, allowing it to rise and double in size.
Preheat your oven to 450°F (230°C) with the Dutch oven or baking stone inside.
Carefully transfer the risen dough to the preheated Dutch oven or baking stone.
Make shallow cuts on the surface of the dough using a sharp knife or razor.
Cover the Dutch oven with its lid or use an inverted pot to cover the baking stone to create steam.
Begin baking with the lid on for 25 minutes, and then proceed by removing the lid and continue baking for an additional 15-20 minutes until the crust achieves a beautiful golden brown color.
Once baked, cool the bread on a wire rack for at least 1 hour before slicing.