Make the dough:
In a large mixing bowl, combine the water, yeast, flour, and salt. Stir together until all combined and no dry bits of flour remain. Mixture will be thick and sticky.
In a separate large bowl, drizzle 2-3 Tablespoons olive oil to coat the bottom. Transfer the dough to the oiled container. Turn the dough so that all sides are coated in olive oil. Cover with plastic wrap or lid. If refrigerating the dough overnight, let rest at room temperature for 30 minutes, then refrigerate for at least 12 hours and up to 48 hours. Dough will rise to double in size. If making focaccia same day, allow dough to rise to double in size at room temperature. about 2 hours.
Remove from refrigerator and allow to rest for 30 minutes in the container, slightly warming up.
Prepare a 9x13-inch pan by coating the bottom and sides with the 2 Tablespoons olive oil and 2
Tablespoons melted butter. Turn the dough out from the container and onto the pan.
Gently stretch the dough to fill the pan. Use the backs of your hands and knuckles to stretch the dough without tearing it. If the dough is springing back and not staying in place, let it rest 10 minutes and come back to it.
In a small bowl, combine the ingredients for the cinnamon sugar filling. Spread half the mixture over half of the dough. Fold the dough in half and rotate it to fit the size of the pan. Gently stretch the dough to fill the pan. Cover with plastic wrap and let rise until puffy and bubbly, about 1 hour to 90 minutes.
Prepare a 9x13-inch pan by coating the bottom and sides with the 2
Tablespoons olive oil and 2
Tablespoons melted butter. Turn the dough out from the container and onto the pan.
Gently stretch the dough to fill the pan. Use the backs of your hands and knuckles to stretch the dough without tearing it. If the dough is springing back and not staying in place, let it rest 10 minutes and come back to it.
In a small bowl, combine the ingredients for the cinnamon sugar filling. Spread half the mixture over half of the dough. Fold the dough in half and rotate it to fit the size of the pan. Gently stretch the dough to fill the pan. Cover with plastic wrap and let rise until puffy and bubbly, about 1 hour to 90 minutes.
Preheat oven to 400.
In a small bowl, combine the ingredients for the crumble topping and set aside. Reheat the cinnamon sugar filling if the butter has solidified.
Drizzle the remaining filling evenly over the top of the dough. Lightly oil your fingertips with olive oil. Gently dimple the dough by pressing into it with your fingertips. Sprinkle the crumble topping over the dough.
Bake for 18-22 minutes.
Place the pan on a wire cooling rack and allow the focaccia to cool for 20 minutes.
While it's cooling, prepare the icing. In a small bowl, whisk together the powdered sugar, vanilla, and milk.
Add just enough milk to make a thick, smooth icing. Drizzle the icing over the focaccia. Let it set for about 10 minutes. Slice and enjoy!
