Cover and cook spinach in a microwave as per instructions until soft, then puree with released water.
Roast cumin seeds in a pan over a low flame until well browned, then grind coarsely. Add to warm spinach puree. Also add the chilli powder, salt, nigella and ajwain seeds.
Add flour a little at a time and knead well for about 5 to 8 minutes to form a soft, firm dough. Add more flour if required.
The dough will keep in the fridge for 3 days, and can be frozen for up to 4 weeks. Cover and leave aside for 20 minutes.
Heat a heavy bottomed pan over medium heat. Knead the dough once more and divide into 12 to 15 balls.
Flatten each ball, and then roll out carefully using flour, into 15cm discs.
Place each paratha on pan, cooking for about 2 minutes on each side, without butter. Then smear with butter on each side and repeat.
The dough should not be sticky. Add more flour if required.