To make the dough:
Put the flour in a large bowl. In a small bowl, combine I cup warm water with the yeast and sugar. Let the yeast proof for about 8 minutes then add the 2 tablespoons olive oil and stir to combine. Pour the yeast mixture over the flour, stirring well to combine. When the dough pulls away from the sides of the bowl, turn it out onto a floured surface and knead the dough until it is smooth and elastic, 5 to 7 minutes.
Put the dough back into a clean large bowl and drizzle with the ½ teaspoon olive oil. Cover the bowl with plastic wrap and let the dough rise in a warm spot until just about doubled in size, about 1 hour. Another way to tell if it’s properly risen: When you poke it with the tip of your finger the dough will not spring back.
To make the topping:
While the dough rises, heat a couple of teaspoons of olive oil in a large sauté pan over medium heat. Add the onions and pepper and cook, stirring every few minutes, until tender, 7 to 9 minutes. Lower the heat to medium-low and let the onions cook until they become golden brown and very soft, another 30 to 40 minutes. Add the garlic, stir to combine, and cook an additional 2 minutes. Let the onions cool.
To assemble and bake:
Heat the oven to 425°F. Oil a 10 × I5-inch sided baking sheet with about 2 teaspoons olive oil. Punch the dough down and turn it out onto a lightly floured surface. Roll the dough out into a rough rectangle measuring about 12 × 18 inches. Fit the dough into the baking sheet, letting the ends of the dough ride up onto the sides of the baking sheet. Drizzle the top of the dough with 2 to 3 teaspoons olive oil. Spread the olive oil over all the dough including the edges. Cover the dough again with plastic wrap and let it relax for about 5 minutes.
Spread the top of the dough with a thin layer of anchovy paste. Spread the onions over the anchovy paste in one layer. Scatter the olives over the top and lay the anchovy pieces—as many as you want—on top of the tart intermittently.
Bake until the crust is browned and crisp, 15 to 20 minutes.