Heat 1 tbsp of the oil or ghee in a large pan over a low-medium heat. Add the onions and sizzle for 15-20 mins until golden brown.
Stir in the garlic, ginger, coriander stalks and cumin seeds. Turn up the heat a little and cook for a few minutes, stirring constantly, until the cumin seeds are aromatic, then add the turmeric, ½ the chilli, coconut milk (reserving 2 tbsp to serve) and spinach. If using fresh spinach, you may have to do this in batches, letting each handful wilt before adding the next. Season well, cover with a lid and cook for 5 mins, then remove the lid and bubble for another 5 mins.
Meanwhile, heat the remaining oil or ghee in a frying pan and cook the paneer for 2-3 mins on each side until browned.
Add half of the coriander leaves to the curry along with the garam masala and a squeeze of lemon juice, then take the pan off the heat and use a hand blender to blitz the curry until smooth and vibrant green. Add a splash of water if the sauce is too thick.
Tip the paneer into the curry sauce and bubble for another minute. Serve scattered with the remaining chopped chilli and coriander leaves, then drizzle with the remaining coconut milk and serve with cooked rice.
