In a large mixing bowl, combine your active sourdough starter with warm water, whisking until well blended. Add salt and unbleached flour, mixing until you form a wet dough. Cover the bowl with a damp towel and allow it to rest for 30 minutes.

After the rest period, perform a set of stretch and folds on the dough. With wet hands, gently lift one side of the dough and fold it over itself, rotating the bowl as you go.

Transfer the dough to an oiled bowl and cover it with the damp towel. Let it rise in a warm area for approximately 3 hours, or until it expands by 50-75%.

Grease a 9x13 glass baking pan with avocado cooking spray to prevent sticking. Gently scrape the risen dough into the pan and perform another set of stretch and folds.

Cover the baking pan with a towel and let the dough proof in a warm spot for about 1 hour.

While the dough is proofing, melt the salted butter in a small saucepan over low heat. Whisk in brown sugar, ground cinnamon, and a splash of vanilla extract until well combined.

After the second proof, use wet fingers to poke dimples into the dough. Pour the buttery cinnamon mixture over the dough, spreading it evenly.

Preheat your oven to 425℉ (220℃). Bake the focaccia for 25-30 minutes, until golden brown.

Once out of the oven, let the focaccia cool slightly before preparing the vanilla icing. Mix powdered sugar with milk or cream until you reach the desired thickness, then drizzle it over the focaccia.