Preheat oven to 180°C.

Trim 4cm off the stalks ends from silver beet and kale; discard. Rinse and drain greens, leaving some water clinging. Tear kale leaves from the centre stem. Cut white stalk from silver beet leaves, cutting into the leaf in a V-shape. Finely chop stems and leaves from greens, keeping them separate.

Heat a large heavy-based saucepan over high heat; cook stems, stirring occasionally, for 10 minutes or until softened. Drain well; transfer to a bowl. Add chopped leaves to pan; cook for 2 minutes or until wilted. Drain well; add to bowl with stems. When cool enough to handle, squeeze excess water from greens (this prevents the pies from becoming soggy).

Combine greens, fetta, green onion, herbs, rind, juice, and egg in a large bowl; season with freshly ground black pepper.

Butter six 2-cup (500ml), 18cm round, 3cm deep pie dishes. Butter half a sheet of pastry, fold in half to make a smaller rectangle; butter top. Place in dish, allowing pastry to overhang edge. Keep remaining sheets covered with baking paper topped with a clean, damp tea towel to prevent them from drying out. Repeat with two more sheets of pastry, stacking them in the dish. You will now have six layers. Place a sixth of the filling into the dish. Brush half a sheet of pastry with melted butter, fold in half crossways, brush with butter, fold in half again; trim to fit the top of the pie. Place over filling, then fold in and scrunch the overhanging pastry. Brush top of pie with a little more melted butter. Sprinkle with sesame seeds. Repeat to make six pies in total.

Sprinkle a little water over each pie; this will prevent the pastry from burning. Bake for 35 minutes or until golden. Serve spanakopitas with lemon wedges.