Five hours before baking the focaccia, line a rimmed baking sheet with parchment paper or a silicone baking mat and oil the bottom and interior sides with the 3 tablespoons olive oil. Begin panning and dimpling the dough, at 20-minute intervals, dipping your fingers in olive oil to keep them from sticking to the dough as you work. After three to four rounds of dimpling and resting, the dough will have relaxed enough to cover the whole pan. At this point, rub the remaining 1 teaspoon of oil over the dough and cover the pan loosely with plastic wrap. Then allow 4 hours for the final rise.
When the dough reaches the rim of the pan, preheat the oven to 475 degrees F (425 degrees F for convection). Carefully peel off the plastic wrap and top the dough with the walnuts, pressing them into the dough. Spread the onion marmalade over the dough. Then top with the blue cheese, spacing the crumbles evenly so that every piece of the focaccia will include a pocket of blue cheese as well as walnuts and onions.
Bake on the middle shelf of the oven for 8 minutes. Then rotate the pan 180 degrees and bake 10 to 12 minutes longer, or until the edge of the focaccia is golden brown and the dough is springy when poked in the center. The undercrust of the focaccia as well as the onions should be caramelized to a golden brown.
Transfer the baked focaccia to the stovetop or to a heatproof counter. Using an offset spatula or bench blade, carefully slide it around the edge, between the crust and the side of the pan, and then lift the focaccia out of the pan and slide it onto a cutting board. If the parchment paper or baking mat is still clinging to the focaccia, remove it. Let it cool for 5 minutes, then cut into 3- or 4-inch squares and serve.
White Flour Master Dough:
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl, combine the flour, salt and yeast. Add all of the water and mix on slow speed for 30 seconds or stir with a large spoon to form a coarse, shaggy dough. Add the 2 tablespoons of oil, increase the speed to medium (or continue mixing with the spoon or with wet hands), and mix for another 30 to 60 seconds to make a wet, coarse, sticky dough. It may seem too wet to form a cohesive dough at this stage. Let the dough rest for 5 minutes to fully hydrate.
Increase the mixer speed to medium-high (or continue mixing by hand) and mix for another 30 to 60 seconds to make a smooth, sticky dough. It should be soft, supple and sticky to the touch, and offer a little resistance when pressed with a wet finger.
Use 1 teaspoon of the extra oil to make a 15-inch-diameter oil slick on the work surface. Rub some oil on a plastic bowl scraper and on your hands and use the scraper to transfer the dough to the oil slick. Stretch and fold the dough. Cover the dough with a bowl and let it rest for 2 to 5 minutes. Repeat the stretch and fold (rub more oil on the work surface as needed), cover the dough, and let it rest for 2 to 5 minutes. Then repeat the stretch and fold, cover with the bowl, and again let it rest for 2 to 5 minutes. Perform a fourth and final stretch and fold to make a smooth ball of dough. The dough will have firmed up after each stretch and fold and will now be soft, smooth, supple, and somewhat sticky but firm enough to hold together when lifted. Transfer the dough to a lightly oiled bowl, cover with plastic wrap, and refrigerate for 12 to 72 hours.
Caramelized Balsamic Onion Marmalade:
In a large frying pan or saucepan, heat the oil over medium heat. When the oil is hot, add the onions, lower the heat to medium-low, and saute, stirring occasionally, for 25 to 30 minutes, or until the onions begin to soften and turn translucent. Do not cook over high heat, as the outside of the onions will char before the interior has softened and sweetened. Continue stirring for another few minutes, until the onions have softened and begin to turn a light amber color. Add the sugar and continue stirring until the sugar melts and begins to bubble. Clear a space in the center of the pan, pour the balsamic vinegar directly into the hot pan, and then stir the onions into the vinegar. Continue stirring for 1 to 2 minutes, until all the onions are coated, and then remove the pan from the heat.
In a mesh strainer set over a clean saucepan, strain the onions, pressing them with a large spoon to release their juice, and wait a few minutes until they stop dripping. Return the strained onions to the saucepan in which they were cooked and set them aside.
Bring the juice to a simmer over medium-high heat, stirring continuously, until thickened. This should take only a few minutes, so don't leave the pan unattended. As soon as the juice thickens into a honeylike syrup, remove it from the heat, pour it all back over the onions, and stir with a rubber spatula until they are coated with the syrup. Stir in the salt and pepper and let the onions cool.
Transfer the mixture to a container, seal tightly, and refrigerate for up to 2 weeks or transfer to sandwich-size resealable freezer bags and freeze for up to 6 months. Defrost at room temperature before using.