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

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

Coat the dough lightly with olive oil, cover with a damp cloth, and refrigerate for at least 12 hours.

Grease a 9x13-inch pan with melted unsalted butter. Deflate the dough and transfer it to the pan, spreading it out. Cover and let rise for 1.5 to 2 hours.

Melt unsalted butter in a saucepan over medium heat until golden brown. Mix in light brown sugar and cinnamon.

Preheat oven to 450°F. Once the dough has risen, press dimples into its surface and drizzle the brown butter mixture over.

Bake for 20-25 minutes until golden brown and edges are crispy. Cool in the pan for 10 minutes before transferring to a wire rack.

For icing, whisk together powdered sugar, milk, and vanilla until smooth. Drizzle over the focaccia and serve.