Spanakopita, the famous Greek phyllo pastry or pie filled with spinach and feta, might be made as small triangular parcels for special occasions or baked in large trays for serving a crowd. This version, baked in and served from a 12-inch cast-iron skillet, is doable for a weeknight dinner, yet is impressive enough for a holiday brunch. For the filling, we combine baby spinach with baby kale, which has a bolder, greener flavor that pairs well with the salty, briny feta. Phyllo is packaged either as 9-by-14-inch sheets or larger 13-by-18-inch sheets. The former can be used as is; the latter should be halved crosswise (use a chef’s knife to simply cut through the stack). You will need a total of eight phyllo sheets. As you make the filling, keep the phyllo covered with a sheet of plastic wrap then a damp kitchen towel to prevent drying. If the sheets tear as you work with them, not to worry. Scrunching them to create a pretty ruffled effect hides flaws.