In France, pissaladiere is a savory tart starring vegetables and herbs. Here we've combined pretty red and yellow sweet bell peppers with onions, Niçoise olives, and herbes de Provence. Anchovies are a secret ingredient that add a layer of flavor, but not so much that you can discern their presence. The mixture is spread on puff pastry dough, and popped in the oven. Cut into bite-sized squares, these make terrific hors d'oeuvres or a savory first course.
Heat the oil in a large skillet over medium heat. When the oil is hot, add the onion, peppers, anchovies, and herbes de Provence. Cooking, stirring frequently, until the onions are golden and the peppers are just tender, about 8 minutes. Add the garlic and continue cooking, stirring frequently, until fragrant, about 2 minutes. Remove the skillet from the heat, stir in the olives, and let the mixture cool.
Position a rack in the middle of the oven and preheat to 400 degrees F.
Place the sheet of puff pastry on a parchment-lined, rimmed baking sheet. Using a fork, poke holes all over the surface of the puff pastry (to prevent it from puffing up excessively). Spread the pepper mixture evenly over the pastry, leaving a 1/4-inch border uncovered on all sides.
Bake until the pastry is puffed and golden brown on the edges, 20 to 25 minutes. If using the parmesan cheese, sprinkle it evenly over the pissaladiere after 20 minutes, then continue baking another 5 minutes.
Transfer to a wire rack and let it cool for 10 minutes. Move the pissaladiere to a cutting board and slice it into squares. Serve warm or at room temperature.