Put the spinach in a microwave safe container and de-frost. Drain any excess water.
Heat oil in a frypan, then add onion and garlic. Cook for 1 minute until softened, then add spinach, pine nuts and dill over a low heat for 1-2 minutes. Combine with cheeses, egg, nutmeg, salt and pepper. Set mixture aside.
Preheat the crisp plate for 2 minutes.
Place one pastry sheet on the crisp plate. Trim into a square shape that fits onto the plate. Use this to measure and trim a second pastry sheet, with an extra 1cm around the edges, and leave that to one side.
Cover the pastry base with the cheese slices and evenly spread the spinach mixture on top.
Cover with the second pastry sheet, using the overhang to pinch the edges together. Prick with a fork and brush with the milk.
Bake for 12 minutes on the crisp function.
You should have enough of the spinach mixture left over to roll up into the last puff pastry sheet. Again bake for 12 minutes. Keep for your lunch the next day.
Cut the square spanakopita into even square pieces and serve with a side salad.