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

In a large bowl, whisk the bread flour and salt. Pour in the yeast mixture and olive oil, stirring until the dough comes together. Lightly grease the surface and cover to rest.

Refrigerate the dough covered for at least 12 hours for slow fermentation to enhance flavor and texture.

Let the chilled dough sit at room temperature while preparing a baking pan lined with parchment and coated in melted butter. Once warmed, deflate it gently, shape it, and place it in the pan to rise for 1.5-2 hours.

Melt unsalted butter in a saucepan over medium heat, stirring until golden brown and nutty. Remove from heat to cool slightly.

Mix cooled brown butter with light brown sugar and cinnamon until smooth and well combined for the topping.

Preheat oven to 450°F. Create dimples across the risen dough's surface, drizzle the topping evenly over it.

Bake for 20-25 minutes until golden brown and crispy on edges. Resist opening the oven too soon!

Whisk powdered sugar, milk, and vanilla extract in a bowl until smooth. Drizzle generously over the slightly cooled focaccia.