Börek is a Turkish pie, commonly savory, made with yufka, a thin dough that’s slightly sturdier than phyllo, and filled with various combinations of meats, cheeses or vegetables. The term “börek” covers a large category of yukfa-based pastries—they may be large and baked, individually sized and fried or formed in a number of different shapes, from spirals to cigars to half moons. For our spinach and cheese börek assembled and baked in a standard 9-by-13-inch baking pan, we use store-bought phyllo instead of hard-to-source yufka, and we modeled it on a recipe from Özlem Warren, author of “Özlem’s Turkish Table.” Phyllo in the U.S. typically is packaged as 9-by-14-inch sheets or larger 13-by-18-inch sheets. The former can be used as is; the latter need to be halved crosswise to fit neatly into the baking pan (use a chef’s knife to simply cut through the stack). You will need a total of 24 phyllo sheets; a one-pound box will contain more than enough. Make sure to fully thaw the phyllo before you attempt to unroll it otherwise the delicate sheets will crack. We like to sprinkle nigella seeds (also known as kalonji) onto the börek just before baking. Black in color and with a savory, herbaceous, oregano-like flavor and hints of allium, they are worth seeking out. If you cannot find them, however, not to worry; simply use a total of 1½ tablespoons sesame seeds. The börek is delicious served warm or at room temperature. Covered tightly, leftovers will keep in the refrigerator for up to three days; reheat in a 350°F oven for 5 to 10 minutes.