Mix flour with butter until there are no lumps of butter left. Add water and sourdough starter and mix until all flour has been hydrated. Let the dough rest for 30 - 50 minutes.

Add salt and perform one stretch and fold. Repeat the stretch and fold after 30 minutes. Let the dough ferment for 3 to 5 hours at a temperature of 78 - 86ºF/25 - 30ºC.

Lightly flour your work surface and dump out the dough. Flatten the dough gently with your hands. Form the dough to a bâtard There's a link to an excellent video showing how to form a bâtard in the recipe notes*.

Let the loaves rise for 1 to 2 hours at 78 - 86ºF/25 - 30ºC, or until they pass the finger poke test**.

Preheat your oven to 480ºF / 250ºC with two oven plates. One to bake the bread on and one just below.

Score the loaves in your preferred pattern and place them in the oven. Pour some water on the plate below and bake each loaf in 25-35 minutes.