- 1/4 cup extra-virgin olive oil
- 1 large Spanish onion, peeled and finely diced
- Coarse salt
- 1 leek (white part only), washed well and thinly sliced crosswise
- Freshly ground pepper
- 1 tablespoon unsalted butter, at room temperature
- 1 cup all-purpose flour
- 3/4 teaspoon baking powder
- 7 ounces Greek yogurt
- 11 ounces feta cheese, crumbled
- 1 cup sautéed spinach, squeezed very dry and chopped
- 1/4 cup chopped fresh dill
- 3 large eggs, at room temperature, beaten
- Heat the oil in a large skillet over medium-low heat. Add the onion and a pinch of salt. Cover and simmer, stirring occasionally, 6 minutes. Add the leek, season with more salt and the pepper, and continue to cook, stirring occasionally, until the vegetables are very soft and translucent, about 8 minutes. Transfer to a bowl and set in an ice bath to cool.
- Meanwhile, preheat oven to 325°F.
- Generously coat an 8-inch round nonstick springform pan with butter and chill.
- Sift together the flour and baking powder in a medium bowl; set aside.
- Combine the yogurt, feta, onion-and-leek mixture, spinach, and dill in a large bowl. Add the eggs and stir to combine. Using a rubber spatula, gently stir in the flour mixture and season with more salt and pepper. Pour into the prepared pan, gently tapping the sides to level the top.
- Bake for 30 minutes. Increase heat to 425°F and bake until golden brown and set in the center, about 10 minutes more.
- Transfer to a wire rack and cool for 10 minutes before unmolding.
- Cut into wedges and serve.