This tart has all the boisterous Mediterranean flavors of pasta puttanesca: tomatoes, anchovies, capers, and olives layered on puff pastry and caramelized onions. Make a tapestry of red, yellow, and orange by layering different-colored heirloom tomato slices over the onions. Though I usually want to put cheese on everything, this tart doesn’t need it. The tomatoes are the stars, so let them shine.
Cooks' Note
You can caramelize the onions ahead if you like.