Make sure the filo is not allowed to dry out as it will make it difficult to coil. Keep covered with a damp tea towel while preparing the rolls.
Make sure that the spinach is well drained of water to ensure that the mixture is not too wet.
Cooking the filo spiral in the cake tin helps keep the coils together but it can also be cooked on a baking sheet
For dairy free make sure the feta is from goats- milk and replace the butter with olive oil.