Prepare your active sourdough starter: Ensure your starter has been fed 4-12 hours prior and is bubbly and active, meaning it has at least doubled in size and floats when a small spoonful is dropped into water.

Add liquids to the bread machine pan: Pour the lukewarm water into the bread machine pan first. Then, spoon in the active sourdough starter.

Add dry ingredients: Add the bread flour on top of the liquid. Create a small well in the center of the flour and add the salt. If using, add the sugar and softened butter into the well or around the edges.

Select the correct setting: Place the pan into your bread machine, close the lid, and select the appropriate 'Sourdough' or 'Artisan Bread' cycle. If your machine doesn't have a specific sourdough cycle, choose a basic white bread cycle, preferably one with a longer knead and rise time. Select your desired crust setting (light, medium, or dark).

Start the machine: Close the lid securely and press start. The machine will now take over the kneading, rising, and baking process.

Monitor and finish: Let the bread machine complete its cycle. Once the baking cycle is finished, carefully remove the bread pan from the machine using oven mitts. Gently turn the pan upside down to release the loaf onto a wire rack.

Cool completely: Allow the sourdough bread to cool completely on the wire rack for at least 1-2 hours before slicing. This is crucial for the texture and flavor to fully develop and prevents a gummy interior.