In a mixing bowl, combine warm water with white granulated sugar. Sprinkle active dry yeast on top and let sit for 10-15 minutes until foamy.

In a large bowl, whisk together bread flour and salt. Pour the yeast mixture and olive oil into the flour mixture and stir to form a sticky dough.

Cover the bowl with plastic wrap and refrigerate for at least 12 hours for the first rise.

Grease a 9x13 inch baking pan, deflate the chilled dough, and stretch it into the pan. Cover and let it rise for 1.5 to 2 hours.

Melt unsalted butter in a saucepan until golden brown; set aside to cool slightly.

Mix light brown sugar and ground cinnamon in a bowl, then stir in the brown butter until dissolved.

Preheat oven to 450°F. Dimple the risen dough and drizzle the cinnamon-butter mixture over it.

Bake for 20-25 minutes until golden brown. Let cool in the pan for about 10 minutes.

Prepare icing by whisking powdered sugar, milk, and vanilla extract until smooth, then drizzle over warm focaccia.