Preheat the oven to 350ºF (180ºC) and grease a 12-inch (30-cm) tart pan with parchment paper. (I tried greasing the pan with oil as per the original recipe, and the tart stuck to the pan).
Cut or break the bread into big pieces and soak it in the milk for 15 minutes, until more or less softened. Stir and break up the bread more as necessary to ensure even soaking.
Drain any excess liquid (I’ve never had any), then process until smooth in a food processor or blender.
Stir in the flour and grated cheese until well incorporated. Add the herbes de Provence, if using. Taste for salt, then stir in the egg.
Spread the batter across the base of your tart pan in a more-or-less even layer with the back of a spoon or by pressing with plastic wrap—the batter is quite sticky.
Blind-bake the crust for about 15 minutes, until completely set and lightly golden around the edges.
Remove from the oven and cover with the onions.
Arrange the olives over the top. If you’re using anchovies, you can add them here, too—I personally prefer to add them after baking.
Bake for 30–40 minutes, until the onions and crust are golden.
Serve warm or at room temperature.