Melt a knob of butter over medium heat in a frying pan, swirling
butter to coat pan evenly. Add onions and fry till onions are soft and
fragrant. Add spinach and fry for a bit. Add feta and stir around for a
bit till cheese starts to melt. Remove from heat and let cool
completely.
In a large bowl, whisk 2 eggs together and add spinach mixture, mixing well. Season with salt and pepper.
Preheat oven to 175C. Line a baking sheet with aluminium foil. Melt
a fair bit of butter in a small bowl. Using a pastry brush, lightly
grease the foil and set baking sheet aside. In a small bowl, whisk the
remaining egg and set aside.
Place 1 filo sheet, long side facing you, on work surface. Brush
lightly with melted butter and place a second sheet of filo pastry over
it, brushing lightly with butter as well. Repeat with the two more
sheets.
Place spinach mixture on prepared filo sheets, closer to one short
end of the sheet than the other but leaving a border all around. Fold
the top and bottom bits over the spinach mixture and then fold the
entire thing across its length. Brush the end of the sheet with the
whisked egg before enclosing spinach mixture completely. Place the
pillow, enclosed side down, on the prepared baking sheet. Brush the top
with the whisked egg and sprinkle sesame seeds.
Repeat with remaining sheets and spinach mixture. Bake for about 20 minutes till pastry is golden brown. Serves 4