Activate Yeast: In a mixing bowl, combine warm water with sugar. Sprinkle yeast, stir gently, and let sit for 10-15 minutes until frothy.

Mix Dough: In a separate bowl, whisk together bread flour and salt. Add yeast mixture and olive oil to the flour. Stir until a sticky dough forms.

First Rise: Cover dough and place in the refrigerator for at least 12 hours.

Second Rise: Preheat oven to 450°F. Grease baking pan with butter, transfer cold dough, dimple it, cover, and let rise for 1.5 to 2 hours.

Prepare Brown Butter: Melt unsalted butter in a saucepan, stirring until golden brown, about 5-7 minutes.

Make Cinnamon Topping: Combine light brown sugar and cinnamon in a bowl, pour in brown butter, and stir until combined.

Dimple Dough: Press deep dimples into the dough surface and drizzle cinnamon-butter mixture over it.

Bake: Bake for 20-25 minutes, until golden brown and puffed.

Finish with Icing: Mix powdered sugar, milk, and vanilla. Drizzle over warm focaccia before serving.