For the topping: In a large skillet, heat the oil over medium-high heat. Add the leeks and season with salt and pepper. Cook, stirring frequently until tender, about 5 minutes. Add the garlic and cook for 30 seconds until aromatic. In batches, add the spinach and cook until wilted, about 5 minutes. Remove the pan from the heat and add the feta cheese and mint. Season with salt and pepper, to taste.
04Using the tines of a fork, prick the surface of the dough all over. Spread the spinach mixture on top and dot with butter.05Bake until the dough is golden and crunchy, 15 to 18 minutes. Cut into squares and serve.