2lgrusset baking potatoes, peeled and cut into 1" piecesto yield 1 1/3 cups mashed
5lgyellow onions, sliced
2tbspolive oil, for caramelizing the onions
1tbspchopped fresh thyme leaves.
2tspactive dry yeast
3 1/2cupsbread flour, divided
1cupwarm water
3tbspextra virgin olive oil
2tspkosher salt
1tspfinishing sea salt like Maldon if desired
Instructions
Boil potatoes in a saucepan, 15 to 20 minutes until fork tender. Drain and mash with a potato masher, hand mixer or ricer until finely mashed and smooth. Set aside to cool.
Meanwhile, place the sliced onions, thyme, and 2 tablespoons of olive oil into a large, high sided skillet and cook on low heat turning often to prevent burning to caramelize to a medium brown color, 30 to 40 minutes. If the onions start to burn, lower the heat. Allow the onions to cool.
In the bowl of a stand mixer, whisk together the yeast, warm water and 1/2 cup of flour and cover for 25 minutes to proof.
Next, add the remaining 3 cups of flour, 1 1/3 cups mashed potatoes, 3 tablespoons of EVOO, and 2 teaspoons of salt to the bowl. Use the paddle attachment to mix this together, 1 or 2 minutes, then switch to a dough hook on medium low speed, #2 KitchenAid, to form a sticky dough ball, 5 minutes.
Place the dough into a large, greased bowl, (small amount of olive oil). The dough is quite sticky so a plastic scraper works well to help remove the dough from the mixing bowl. Cover loosely with a towel , place in a warm spot and let rise to double the size, 45 to 60 minutes.
Grease a 12" by 17" baking sheet, (olive oil again), place the dough on the sheet and press the dough to cover the sheet. This is a little like pizza dough and will spring back some. Use your fingertips to coax in into place. Cover loosely and let rise 35 minutes.
Preheat oven to 425°.
Next, lightly oil the top of the dough with olive oil, then use your fingertips to make lots of indentations in the dough. Top the dough with the cheese followed by the onions. I then lightly sprinkled with sea salt.
Place in the oven 20 to 24 minutes, turning the pan once at 10 minutes to ensure even browning. Bake until nicely browned. Remove from the oven and place the sheet pan on a cooling rack. After 5 minutes or so, use a couple of large spatulas to remove the focaccia from the pan and then let it cool on the rack. (Removing the bread from the pan right away will prevent the bottom crust from getting moist or soggy).Slice and serve warm.
Notes
Nutrition information is based on cutting 12 large servings. Smaller portions are also possible.