Make the dough: Whisk together the yeast and 1 cup water, heated to 115°F, in a large bowl; set aside until foamy, about 10 minutes. Add the flour, ¼ cup oil, and salt; stir until a dough forms; transfer to a lightly floured work surface and knead until smooth, about 6 minutes. Transfer to a greased bowl, cover with plastic wrap, and set aside until doubled in size, about 1 hour.
Meanwhile, make the topping: Heat the remaining ½ cup oil in a 6-quart saucepan over medium-low; add the anchovies and cook, stirring, until dissolved in the oil, about 7 minutes. Add the onions, thyme, rosemary, and bay leaves, season with salt and pepper, and cook, covered and stirring occasionally, until reduced and softened, about 1 hour; uncover and cook, stirring occasionally, until the liquid evaporates and the onions are golden brown, about 30 minutes. Remove from the heat and discard the herbs; let cool.
Preheat the oven to 425°F. Uncover the dough and transfer to a lightly floured work surface; using a rolling pin, roll the dough into a 12-by-18-inch rectangle. Transfer to a greased 13-by-18-inch rimmed baking sheet, then cover evenly with the onion mixture; place the olives decoratively over the top. Loosely cover with plastic wrap and set aside until the dough is puffed, about 1 hour. Bake until the tart is golden brown at the edges, about 20 minutes. Let cool for 10 minutes before cutting into squares to serve.