Step 1

Defrost the spinach and phyllo dough in the fridge overnight.

Step 2

For the filling, heat the olive oil in a medium skillet over medium heat. Add the onion, season with salt and pepper and cook until softened and lightly golden brown, about 5 minutes. Add the garlic and cook for 1 to 2 minutes, stirring frequently. Then remove the pan from the heat and stir in the parsley, dill, red pepper flakes, nutmeg and lemon zest. Set aside to cool to room temperature.

Step 3

Meanwhile, preheat the oven to 350 degrees F (175 degrees C). Drain the spinach through a strainer lined with a clean kitchen towel or a few layers of sturdy paper towel. Gather the spinach up in the towel and squeeze out as much of the water as possible. Transfer to a bowl and add the lemon juice and feta. Stir in the cooled onion mixture and the egg.

Step 4

Retrieve the phyllo from the fridge, unroll it and cover it with a clean kitchen towel to keep it from drying out. Place a 9-inch springform pan on a rimmed baking sheet and brush the bottom and sides lightly with butter. Lay out one sheet of phyllo, brush with butter and transfer it to the prepared pan. There is no need to be extra careful here – the phyllo might tear, crack or rumple up a bit but that just makes for more texture in the end result. Layer on two more buttered sheets of phyllo across the bottom of the pan.

Step 5

Continue buttering the phyllo as before but begin placing the remaining sheets off-center around the pan so that their edges overlap in the center of the base and the other edge hangs over the sides, gently pressing along the bottom and up the sides to create a crust. Transfer the spinach filling into the phyllo crust and spread into an even layer.

Step 6

Gather and fold the overhanging phyllo overtop of the edges of the spinach, leaving the center bit of spinach exposed. Brush the phyllo with remaining butter and bake for 40 to 50 minutes, or until golden brown and crisp. Allow to cool slightly before removing from the pan and serving.