Combine sourdough starter with lukewarm water, mix until dissolved, then add bread flour and salt. Let rest for 30 minutes.

Perform stretch-and-fold technique, then cover and let rise for 8 hours until doubled in size.

Cover dough tightly with plastic wrap and refrigerate overnight for at least 8 hours.

Preheat oven to 450°F. Drizzle baking pan with olive oil, transfer dough upside down, and shape into a rectangle.

Fold the edges toward the center and flip the dough over. This builds surface tension.

Cover dough and let rise for 4 hours until it spreads and nearly doubles.

Preheat oven to 450°F. Ensure a high temperature for crispy crust.

Drizzle olive oil on surface and create dimples with fingertips. Sprinkle with rosemary and finishing salt.

Bake for 25-30 minutes until golden brown and crispy.

Melt butter, add garlic and parsley, and brush the mixture over warm focaccia after baking.

Let cool for 30 minutes, slice, serve, and enjoy!