In a mixing bowl, combine warm water with granulated sugar, then sprinkle yeast on top. Allow to sit for 10-15 minutes until foamy.

In a large bowl, whisk together bread flour and salt. Add the yeast mixture and olive oil. Stir until a sticky dough forms.

Cover the bowl with a damp towel and refrigerate for at least 12 hours for the first rise.

Grease a baking pan with melted unsalted butter. Transfer chilled dough to the pan and let it rise in a warm spot for 1.5 to 2 hours.

Melt brown butter in a saucepan, remove from heat, and stir in brown sugar and cinnamon. Set aside.

Preheat oven to 450°F. Press dimples into the risen dough and drizzle with the cinnamon-butter mixture.

Bake for 20-25 minutes until golden brown. Let cool in the pan for 10 minutes before transferring to a wire rack.

Prepare icing by whisking powdered sugar, milk, and vanilla extract. Drizzle over slightly cooled focaccia and slice.