Potato and Leek Focaccia

Preparation

1. Step 1

   Combine the water, yeast and sugar together in a large bowl. Let sit until the yeast is activated and foamy, 5 to 10 minutes.

2. Step 2

   Stir in the flour and salt to make a shaggy, sticky dough. Pour 2 tablespoons of olive oil over the dough and turn to coat the dough with oil. Cover the bowl with plastic wrap and refrigerate for 18 to 24 hours.

3. Step 3

   When you are ready to bake, coat a metal 9-by-13-inch baking pan with butter and pour 2 tablespoons oil into the pan. Gently fold the dough over itself a few times in the bowl, then transfer it to the prepared pan and turn it over to coat with oil. Arrange the dough seam-side down and let it rise, uncovered, until it almost covers the bottom of the pan, about 2 hours.

4. Step 4

   Just before the dough has finished rising, heat your oven to 425 degrees and set a rack in the center.

5. Step 5

   When you are ready to bake, combine the sliced leeks and potatoes in a large bowl. Strip the leaves from the thyme and add them to the bowl along with the remaining 1 tablespoon oil and a sprinkle of salt and pepper; toss to combine evenly.

6. Step 6

   Use your fingertips to dimple the dough and gently push it to evenly cover the bottom of the pan. Arrange the leeks and potatoes in an even layer over the dough. Bake until the focaccia is golden on the edges and the leeks begin to brown, about 30 minutes.

7. Step 7

   Sprinkle the top with cheese and bake for 5 minutes more. Let cool slightly before serving.