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

In a large mixing bowl, whisk together bread flour and salt. Create a well in the center, then pour in the yeast mixture and olive oil. Stir with a wooden spoon until a sticky dough forms.

Cover the bowl with plastic wrap and refrigerate for a minimum of 12 hours.

Prepare a greased 9x13-inch baking pan and pour melted butter into the center. Transfer the chilled dough into the pan and let it rise for 1.5 to 2 hours.

Melt unsalted butter over medium heat until golden-amber. Remove from heat and allow to cool slightly.

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

Preheat oven to 450°F. Create dimples all over the dough and drizzle the cinnamon mixture over the dough. Bake for 20-25 minutes until golden brown.

Prepare the icing by mixing powdered sugar, milk, and vanilla extract until smooth. Drizzle over warm focaccia.