2) Mix the dough on medium-low speed for about 10 minutes, until smooth, sprinkling it with flour to keep it from sticking to the bowl. When the dough is ready, turn it out onto a floured board and knead it by hand a dozen times. It should be smooth and elastic.
3) Place the dough in a well-oiled bowl and turn it to cover lightly with oil. Cover the bowl with a damp kitchen towel. Allow to rest at room temperature for 30 minutes.
4) Preheat the oven to 220°C/gas mark 8. Divide the dough into 2 equal parts, rolling each into a smooth ball. If you're only making 1 pissaladiere, place 1 ball on a baking sheet and cover it loosely with a damp towel. Allow the dough to rest for 10 minutes. (If you're not using the other dough straight afterwards, wrap it well and refrigerate or freeze for next time.)
5) Roll the dough lightly with a rolling pin, then stretch it to a 25cm square and place it on a baking sheet sprinkled with cornmeal.
For the topping:
1) Heat the olive oil in a very large saute pan and cook the onions, thyme, salt, pepper and garlic over a low heat for 45 minutes, until the onions are sweet and cooked but not browned. Toss the onions from time to time. After 30 minutes, remove the garlic, chop it roughly, and add it back to the onions.
2) Spoon the onion topping onto the dough, leaving a 2cm border all around. Artfully arrange the anchovies and olives on top. Brush the edge of the dough with olive oil, and bake for 15 minutes, or until the crust is crisp. Serve hot on a cutting board.