In a large mixing bowl, combine active sourdough starter and water. Whisk to combine until starter is evenly dissolved.

Add salt and flour to mixture and whisk to combine to form dough. Dough will be very wet and sticky and not come together right away. This is normal! Let dough rest for 30 minutes.

After 30 minute rest, perform 1 set of stretch and folds.

Spray 2nd mixing bowl with avocado cooking spray. Transfer dough to greased mixing bowl and cover with a damp kitchen towel. Let dough sit covered for about 3 hours or until the dough has grown in size by 50% to 75%.

Once dough is proofed, spray 9x13 glass baking pan with avocado oil. Transfer dough to greased baking pan and do 1 set of stretch and folds once more.

Cover the dough and refrigerate it overnight or up to 12 hours before proceeding with a 2nd proof and baking.

Cover pan with damp kitchen towel. Place pan back in oven with the oven light on for a 2nd rise for 1 hour or until the dough has nearly doubled in size.

In a small saucepan, melt butter over medium heat. Add brown sugar, cinnamon, and vanilla extract. Whisk to combine and remove from heat.

Wet fingers and poke the dough to create 'dimples.' Gently push the dough all over to expand it fully in the pan.

When the oven is preheated to 425℉, pour cinnamon sugar topping all over dimpled dough in the pan. Bake for 25-30 minutes until focaccia is bubbling and golden brown.

While focaccia is cooling in the pan, mix together glaze. Combine powdered sugar and vanilla extract in a small bowl. Add milk or cream a little at a time until you've reached your desired glaze consistency. Drizzle glaze over slightly cooled focaccia. Slice, serve, and enjoy!