Preheat oven to 180°C (355ºF). Layer the filo sheets, brushing with butter between each layer. Cut the sheet into 6 pieces and press into 6 x ½ cup-capacity (125ml) lightly greased muffin tins. Bake for 6–8 minutes or until crispy and golden. Set aside.
Heat a large non-stick frying pan over medium heat. Add the butter, spinach, pine nuts, lemon zest, salt and pepper and cook for 3–4 minutes or until the spinach is just wilted. Spoon the spinach mixture into the filo cups and top with feta to serve. Makes 8.