In a small bowl, combine 1 cup of warm water with 2 tablespoons of granulated sugar. Sprinkle 2 teaspoons of active dry yeast over the water and let it sit for 10–15 minutes until foamy.

In a large mixing bowl, whisk together 3 cups of bread flour and 1 teaspoon of salt. Create a well in the center and pour in the activated yeast mixture along with 2 tablespoons of olive oil. Stir until a sticky dough forms.

Cover the bowl with a clean kitchen towel and place it in the refrigerator for at least 12 hours.

Grease a 9x13-inch baking pan and pour in the remaining melted butter. Gently deflate the dough and transfer it into the prepared pan.

Melt 4 tablespoons of unsalted butter in a saucepan. Cook until golden-amber and allow it to cool for about 10 minutes.

Mix together ½ cup of light brown sugar and 2 teaspoons of cinnamon in a bowl. Pour this mixture into the cooled brown butter and stir until smooth.

Preheat your oven to 450°F. Use your fingers to gently press dimples all over the surface of the dough. Drizzle the cinnamon-butter mixture over the dimples.

Bake for 20–25 minutes until the top is golden brown. Let cool in the pan for about 10 minutes.

Prepare the icing by whisking together 1 cup of powdered sugar, 2 tablespoons of milk, and 1 teaspoon of vanilla extract until smooth. Drizzle over the cooled focaccia.