Spanakopita Slab

Ingredients

• 1 kg frozen chopped spinach, fully defrosted
• 300 g feta, crumbled
• 250 g ricotta
• 3 large eggs
• 1 bunch spring onions (about 8), finely sliced
• 30 g fresh dill, finely chopped
• 20 g flat-leaf parsley, finely chopped
• 1 lemon, zest only
• ¼ tsp freshly grated nutmeg
• black pepper, generous
• sea salt, to taste (go light; feta is salty)
• 500 g filo pastry (1 standard pack), at room temperature
• 175 g unsalted butter
• 5 tbsp olive oil, divided
• 1 tbsp sesame seeds, for the top
• 1 tsp nigella seeds, for the top

Method

1. Defrost the spinach completely, then squeeze it out in batches in a clean tea towel. Squeeze hard. You want it almost dry. Wet spinach means a soggy slab, and there's no recovering from that. You should end up with roughly 500g of tightly packed squeezed spinach from the kilo you started with.
2. Heat the oven to 180°C fan. Brush a large baking tray (roughly 30x40cm with a 4–5cm lip) with a little melted butter.
3. Melt the butter in a small pan and stir in the olive oil.
4. Tip the squeezed spinach into a large bowl and break it up with your fingers so there are no compressed clumps. Add the crumbled feta, ricotta, eggs, spring onions, dill, parsley, lemon zest, nutmeg, 2 tbsp olive oil and a heavy crack of black pepper. Mix thoroughly. Season lightly. Feta varies wildly in saltiness, so add only a small pinch if the filling needs it.
5. Unroll the filo and keep it under a slightly damp tea towel while you work. Filo dries to brittle confetti within minutes of being exposed to air; this is the single most common spanakopita disaster.
6. Lay the first sheet into the tray, letting any excess drape over the sides. Brush generously with the butter-oil mix, right to the edges. Repeat with half the filo sheets; usually 8 to 10; buttering between each one. Don't be precious about tears or wrinkles; the layered crinkles are what give spanakopita its shatter and character.
7. Spread the filling evenly across the buttered base, right into the corners, and level the top with the back of a spoon.
8. Layer the remaining filo sheets on top, buttering between every single one. The butter between layers is what creates the crisp; skip a sheet and you get a doughy band running through the middle of the slab.
9. Tuck the overhanging edges down the sides and into the tray to seal the filling in. Brush the top generously with the last of the butter-oil.
10. Use a sharp serrated knife to score the top into squares or diamonds through only the upper filo layers; do not cut into the filling. Scoring now lets steam escape cleanly and means you can cut neat squares once it's cooled without the top shattering everywhere.
11. Scatter the sesame and nigella seeds over the top and flick a few drops of water across the surface; the water turns to steam in the oven and helps the top crisp evenly rather than browning in patches. Finish with a small pinch of flaky salt over the seeds.
12. Bake for 45–55 minutes, until the top is deep golden brown and the slab feels firm and sounds hollow when tapped in the centre. If it's browning too fast at the 30-minute mark, drop the heat to 170°C fan.
13. Cool the slab in the tin for at least 30 minutes before cutting. Slicing hot means a collapsed mess and a runny filling; it firms up beautifully as it cools and is genuinely better at room temperature than straight from the oven, which is exactly why it's a picnic legend.
14. Cut down through the scored lines with a serrated knife in a long sawing motion, and lift the squares out with a palette knife. Pile the squares onto a platter and serve warm or at room temperature, while the filo is still crisp.