In a small bowl, combine the warm water and granulated sugar. Sprinkle the active dry yeast over the top and let it sit for 10-15 minutes until it becomes foamy.

In a large mixing bowl, whisk together the flour and salt. Pour in the activated yeast mixture along with the olive oil. Stir until a sticky dough ball forms. Lightly rub the surface of the dough with olive oil.

Cover the bowl with a damp tea towel or plastic wrap. Place it in the refrigerator for at least 12 hours.

Grease a 9x13-inch baking pan and line it with parchment paper. Pour 2 tablespoons of melted butter into the center of the pan. Gently deflate the dough by pulling it from the sides of the bowl and folding it toward the center several times. Place the dough into the buttered pan, cover, and let it rise for 1 ½ to 2 hours in a warm spot.

In a small saucepan, melt ½ cup of butter over medium heat. Stir continuously until it develops a nutty aroma and turns a golden-amber color. Remove from heat immediately to prevent burning. Allow it to cool for 10 minutes.

In a bowl, mix the brown sugar and cinnamon into the browned butter until the sugar dissolves.

Preheat your oven to 450°F. Once the dough has risen, use wet fingertips to press deep dimples all over the surface. Drizzle the cinnamon-butter mixture evenly over the dimpled dough.

Bake for 20-25 minutes, or until the focaccia is golden brown. Let it cool in the pan for 10 minutes before transferring it to a cooling rack.

In a bowl, combine the powdered sugar, milk, and vanilla extract. Mix until smooth. Drizzle the icing evenly over the warm focaccia, slice into squares, and enjoy!