Feta date spinach pastries

Name: Feta, date & spinach pastries
Ingredients: 500g spinach any coarse stalks removed; 115g butter; 1 tbsp olive oil; ½ small onion finely chopped; 2 garlic cloves crushed; 4 spring onions finely chopped; 8 dates stoned and finely chopped; ½ small bunch of parsley leaves finely chopped; 8 mint sprigs, leaves torn; 25g toasted pine nuts; 150g feta crumbled; 1 medium egg lightly beaten; 250g pack filo pastry sheets; black sesame seeds for sprinkling