Add the spinach, feta, dill, mint, lemon zest, nutmeg and eggs to the bowl with the potato and leek. Season generously. Layer up 7 sheets of filo in the cake tin, brushing a little oil between each sheet, making sure the layers overlap and leaving overhanging pastry over the edges. Transfer the potato mixture to the centre of this then top with the final filo sheet. Bring the edges of the filo in to cover the topping and brush with a little extra olive oil. Scatter over the sesame seeds, transfer to a baking sheet and bake on the top shelf of your oven for 35-40 minutes, until deep golden brown.