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

In a large bowl, whisk together bread flour and salt. Create a well in the center and pour in the yeast mixture along with olive oil. Stir until the dough is slightly sticky.

Transfer dough to a lightly oiled bowl, cover with plastic wrap, and refrigerate for at least 12 hours for slow fermentation.

After resting, take the dough out and let it warm up for 30 minutes. Shape it and press into a greased baking pan, cover with a cloth and let it rise for 1.5 to 2 hours.

In a small saucepan, melt unsalted butter over medium heat until browned. Stir in light brown sugar and cinnamon until smooth.

Preheat oven to 450°F. Make dimples all over the risen dough and drizzle the brown butter topping over. Bake for 20-25 minutes until golden brown.

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