In a small bowl, combine warm water with granulated sugar. Sprinkle active dry yeast over the top, gently stir, and let sit for 10-15 minutes until frothy.

In a large bowl, whisk together bread flour and salt. Pour in activated yeast mixture along with olive oil. Stir until sticky dough forms.

Refrigerate dough for at least 12 hours, then let it sit at room temperature for 20 minutes.

Grease a 9x13 inch pan and transfer the chilled dough to it. Let it rise covered for 1.5 to 2 hours.

Melt butter in a saucepan until golden brown. Let cool.

Combine light brown sugar and cinnamon with cooled brown butter. Mix until smooth.

Dimple risen dough, drizzle the cinnamon topping over it.

Preheat oven to 450°F. Bake for 20-25 minutes until golden brown. Cool for 10 minutes then transfer to a wire rack.

Mix powdered sugar, milk, and vanilla for icing. Drizzle over the warm focaccia.