2 tbsp. extra-virgin olive oil
2 teaspoons minced fresh thyme
2 large red onions, halved length-wise and thinly sliced
2 teaspoons sugar
1 teaspoon red wine vinegar
kosher salt and freshly ground black pepper, to taste
10 salt-cured black olives, pitted and minced
2 sheets 2 (9" x 11") frozen puff pastry, thawed
8 oil-packed anchovies filets, drained, cut into 4 slivers each
minced chives or flat-leaf parsley, for garnish
Heat oil in a 12" skillet over medium heat. Add thyme and onions and cook, partially covered, stirring occasionally, until very soft, 30 -45 minutes.
Increase heat to medium-high, add sugar and vinegar, and season with salt and pepper. Cook, stirring, until caramelized, 12–15 minutes.
Stir in olives, remove from heat, and set aside until totally cool. (filling and dough can be made a day ahead as long as dough is softened up before rolling)
Meanwhile, heat oven to 400°.
Roll out puff pastry or basic tart and pie dough to 1/8" thickness. Using a 2 1/2" cookie cutter, cut out 16 circles from each sheet.
Transfer pastry circles to 2 parchment paper—lined baking sheets and prick each circle all over with tines of a fork. Cover circles with a sheet of parchment and another baking sheet; bake until light golden brown, 15–18 minutes.
Uncover, spoon about 1 tsp. onion mixture over each, and top with a sliver of anchovy and sliced olives then bake an additional 15 minutes until golden brown, 2–3 minutes more.
Transfer circles to a large serving platter, . Garnish with chives.
