Preheat oven to Gas Mark 6, 200ºC, fan 180ºC. To make the filling, place a baking tray in the oven to heat. Put the spinach in a bowl and pour over boiling water to wilt the leaves. Drain, rinse in cold water and use your hands to squeeze out all the liquid. Chop and set aside.
Heat the oil in a frying pan over a low heat. Add the onion and garlic and season with salt and pepper. Cook for 10 minutes until soft and golden, then add the spinach, paprika and cumin seeds. Cook for 5 minutes. Stir in the pine nuts and dates then transfer to a bowl to cool.
Brush a sheet of pastry with butter then slice vertically into 3 strips. Cover remaining pastry with a damp tea towel. Place a heaped teaspoon of filling at the bottom left side of the strip.
Gently take the lower right corner of the pastry and fold it over and up to cover the filling. You should now have a triangle left at the bottom of the pastry strip.
Take the lower tip of the triangle, fold over and up. Continue folding, then brush with butter.
Repeat with the remaining ingredients. Place the finished triangles seam-side down on a preheated tray; bake for 15 minutes or until golden brown.