Leftover lamb pie

Name: Leftover lamb pie
Ingredients: 2 sticks of celery; 2 leeks; 2 onions; 3 cloves of garlic; 1 kg leftover roast lamb; 75 g unsalted butter , plus extra (melted) for greasing and layering; 3 tablespoons olive oil; 500 g potatoes; 180 g long grain rice; ½ a bunch of fresh flat-leaf parsley; 3 large free-range eggs; 300 g feta cheese; 60 g currants or raisins; ½ tablespoon ground cinnamon; 1 tablespoon dried oregano; 1 tablespoon dried mint; 2 x 270 g packets of filo pastry; 1 tablespoons za'atar