Heat butter in a pan. Crackle jeera and add hing to it. Add chopped onions and saute until pink. Add ginger-garlic paste and cook. Add the tomato puree and cook until all water evaporates and the cooking gravy starts leaving oil /butter.
Then add salt and garam masala.
Add cream and let it cook for a minute.
Add the spinach puree.
Stir well
The gravy is ready.

FOR TANDOORI AALOO,
You can prepare in two ways..
1. You can take raw potatoes,peeled and cut into cubes. Deep fry them till golden brown and then sprinkle tandoori masala over it.
2. I used this way.. Take parboiled potatoes, cut them into cubes. Put these cubes in a bowl containing 1 tbsp curd + garam masala + 2 tsp besan. Shallow fry these cubes on a nonstick skillet till golden brown.

Add these tandoori aalo in gravy and serve hot with parathas