2 tbsp. extra-virgin olive oil, plus more for drizzling
1 medium yellow onion, diced (1 cup)
1 medium bulb fennel, quartered, cored, and thinly sliced (3.4 cup)
3 cloves garlic, finely chopped (1 Tbsp.)
1 medium bunch Lacinato kale, stems removed, chopped into bite-sized pieces (6 cups)
1⁄3 cup crumbled feta cheese, plus more for topping
1⁄4 cup kalamata olives, pitted and finely chopped
2 tbsp. coarsely chopped fresh parsley
Fresh ground black pepper
1 (17-oz.) package (2 sheets) all butter puff pastry, thawed in the fridge overnight
3 tbsp. unsalted butter, melted
Directions
Heat the oil is a large skillet over medium heat. Add onion and cook, stirring occasionally, until softened and lightly browned, 5-7 minutes. Add fennel and garlic and cook, stirring occasionally, until softened, 8–10 minutes. Lower heat; add kale, cover pan and cook until kale is soft and wilted, adding a teaspoon of water if necessary, about 5 minutes. Remove pan from heat and fold in feta, olives and parsley. Season with pepper to taste.
Preheat oven to 375° and line two baking sheets with parchment paper. Lightly flour a work surface and unroll one of the pieces of puff pastry. Use a rolling pin to sheet the dough out to a 14–inch square, then cut the sheet into nine equal squares. Cut L-shaped slits on opposite corners of each square (creating a frame-like shape). Take hold of both corners and fold them toward the opposite corner, passing one point under the other and pressing them in place, to create a diamond-shaped pocket to hold the filling. Repeat the process with the second sheet of dough, then divide the pastries between the prepared baking sheets, leaving at least 1 1⁄2 inches between each pastry.
Mound 2 generous tablespoons of filling into each pocket; top with a little more feta and a drizzle of olive oil. Brush the outer edges with melted butter, then transfer to the oven and bake until evenly golden brown and puffed, 25–30 minutes. Serve warm, topped with more feta if you like.