To a pot of boiling water, add little salt and then spinach leaves to it. Blanch the spinach leaves for 2 to 3 minutes until wilted.
Take them out and put them in ice cold water. This helps the leaves in retaining their green color.
To a blender, add the blanched spinach along with tomato, 3 cloves of garlic, ginger and green chili. Puree to a smooth paste and set aside.
Heat a pan on medium heat. Once hot, add the oil and then add the remaining 2 cloves of chopped garlic. Sauté for few minutes until it starts changing color.
Then add the chopped onions. Cook the onion for 2 to 3 minutes until soft and translucent.
Add in the prepared spinach puree and mix. Also add around 1/2 cup water at the point.Cover the pan and let it cook for 10 minutes on medium heat. The spinach will bubble a lot. Stir at regular intervals to avoid sticking at the bottom.
Once the spinach is cooked, add the garam masala, turmeric powder, red chilli powder and salt. Mix and cook for 1 minute.You may also add ½ teaspoon of sugar at this point if you like.
Then add the heavy cream and mix.
Stir in the paneer and mix. Let the curry simmer for 3 to 4 minutes. Switch off the flame, add lemon juice and kasuri methi and mix.
Serve palak paneer hot with naan or roti or rice.
If the spinach is bitter, you can use 1/2 teaspoon of sugar. That's totally optional.
If you like, you can pan-fry the paneer cubes (until golden brown) before adding them to the curry.