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

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

Cover the dough with plastic wrap and let it rest in the refrigerator for at least 12 hours.

Grease and line a baking pan with parchment paper, pour in melted unsalted butter, and spread the chilled dough over it. Let it rise in a warm place for 1.5 to 2 hours.

Melt unsalted butter over medium heat until golden brown, then let cool slightly.

Mix light brown sugar and cinnamon with cooled brown butter until well combined.

Preheat the oven to 450°F (230°C). Press dimples into the risen dough and drizzle the cinnamon-butter mixture over the top.

Bake for 20-25 minutes until the top is golden brown. Allow to cool slightly.

Mix powdered sugar, milk, and vanilla extract to make icing, then drizzle over the warm focaccia before slicing.