Makes one 9-inch x 13-inch loaf
Be patient, and plan wisely. Depending on the temperature and humidity in your house, it’ll take a few hours for the dough to rise sufficiently—don’t skimp on this step, unless flat, dense focaccia is your goal. The one I made a few days ago took 3 full hours since our temperatures dropped dramatically earlier this week. That time would be significantly less on a hot, humid summer day. You can experiment with making the dough the night before, and letting it ferment in the fridge. You’ll need to give it time to come to room temperature, and rise in the pan, so it’s not like you’d save any time. The overnight fermentation would develop the flavors a bit, though, so it’s worth a try.
2 1/2 cups (450 grams) “00” flour, plus more for kneading
1 teaspoon (4 grams) instant yeast (I use Red Star)
1 teaspoon (6 grams) fine sea salt
1 1/2 to 2 cups (225 to 300 grams) warm water
1 cup (230 grams) cold, cooked mashed potatoes
Extra virgin olive oil, for drizzling
Coarse sea salt, to taste
Add the flour, yeast, and salt to a deep bowl. Whisk to combine.
Add 1 1/2 cups of the warm water. Stir until it forms a scraggly-looking dough. Add the mashed potatoes, and stir until the dough becomes smoother. You may need some (or all) of the remaining water, depending on how wet your potatoes were before adding them to the dough.
Lightly flour a counter or cutting board. Turn the dough out onto the counter, and sprinkle with a bit more flour. Knead, adding more flour, as needed, until the dough is smooth, and no longer sticky.
Grease the bottom and sides of a 9-inch by 13-inch by 2-inch. Press the dough into the pan, all the way to the sides. Cover the pan tightly with plastic wrap, and then drape a towel over it. Set the pan in warm (not hot) spot, until the dough has tripled in volume, (it should rise almost to the top of the pan).
30 minutes before the dough looks ready, preheat the oven to 450ºF.
When ready to bake, use the end of a wooden spoon to poke holes into the dough (the dough will deflate slightly; don’t worry). Drizzle olive oil and some salt on top.
Bake on the center rack of the oven until deep golden brown and hollow when tapped with the tip of your finger, about 25 minutes.
Let cool at least 10 minutes before serving (30 minutes is preferable if you can wait that long).