ONION AND ROSEMARY FOCACCIA
- Small Saucepan
- Handheld Blender
- 2 Large Bowls
- Half-Sheet Pan
- 1 Small Russet Potato
- 2½ Cups Cold Water
- 5 Cups All-Purpose Flour
- 2½ tsp. Active Dry Yeast
- 1 tsp. Sugar
- Kosher Salt
- 2 Tbsp. Olive Oil Plus More For Oiling The Pan
- 1 Small Sprig Fresh Rosemary
- 2 Small Sweet Onions Thinly Sliced
- 3 Tbsp. Olive Oil
- ¾ tsp. Flaky Sea Salt
- Peel the potato and cut into 1-inch cubes. Combine the potato and 2½ cups cold water in a small saucepan, cover, and bring to a boil. Boil the potato until very tender when pierced with the tip of a knife, about 15 minutes.
- Use a handheld blender to purée the potatoes and cooking liquid to a smooth slurry (alternately, run the mixture through a food mill or mash with a fork until as smooth as possible). Let cool until just warm (the water should not be boiling hot when added to the yeast).
- Meanwhile, whisk together the flour, yeast, sugar, and 1½ teaspoons salt in a large bowl.
- Add the olive oil and the warm potato mixture and stir until the dough just comes together (it will be very soft and sticky).
- Generously oil a large bowl and transfer the dough to it, rolling the dough around to coat it in the oil. Cover tightly with plastic wrap and set aside at room temperature to rise until doubled in size, about 1 hour.
- Strip the rosemary leaves and coarsely chop them. Combine the rosemary, onions, and olive oil in a bowl and toss together.
- Heat the oven to 400°F. Lightly oil a half-sheet pan, then scrape the dough onto the pan. With lightly oiled fingers, stretch and pull the dough to fill the pan. Press your fingertips into the dough to create deep dimples. Scatter the onion mixture evenly over the dough, drizzling any remaining oil over everything. Sprinkle the sea salt over the topping.
- Cover the pan with a clean kitchen towel and let rise until the dough is almost level with the sides of the pan, about 1 hour.
- Bake the focaccia until golden brown, 35 to 40 minutes. Remove from the oven and let cool a few minutes before cutting into big squares.