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

In a large bowl, whisk bread flour and salt. Create a well, pour in the yeast mixture and olive oil, and stir until sticky dough forms.

Knead the dough on a floured surface for 5 minutes. Shape into a ball, place in a greased bowl, cover with a towel, and refrigerate for at least 12 hours.

Deflate the dough and transfer to a greased baking pan. Press to fit the pan and create dimples. Cover and let rise for 1.5 to 2 hours.

Melt unsalted butter in a skillet over medium heat, stirring for 5-7 minutes until golden-amber. Remove from heat and cool slightly.

In a bowl, combine light brown sugar and cinnamon. Stir in the warm brown butter until well combined.

Press fingers into the risen dough to create dimples. Drizzle the cinnamon-brown butter mixture over the surface.

Preheat oven to 450°F. Bake focaccia for 20-25 minutes until golden-brown and fragrant.

Mix powdered sugar, milk, and vanilla extract until smooth. Drizzle over the baked focaccia after cooling.