I made Bombay aloo last night which turned out fantastic. You might want to try this recipe adding spinach as well to make a sag aloo.
The original recipe was courtesy of Curry Cannuck, but I modified it slightly as below.
3 tablespoons oil
1 1/2 teaspoons mustard seeds
1 teaspoon ground cumin
1 teaspoon turmeric
1 teaspoon ground coriander
1 teaspoon garam masala
1/4 teaspoon hot chili powder and 1 fresh green chili finely chopped
2 inch fresh ginger, peeled and grated
4 tablespoons butter
6 potatoes, peeled, parboiled and cut into cubes
2 cloves of garlic peeled, crushed and finely chopped
4 tomatoes, diced
1 cup fresh coriander, roughly chopped
1/2 tsp salt (seasoning)
Heat the oil in a pan and fry the spices for a few minutes. Add the butter, then the potatoes and garlic making sure they are completely coated in the spice mixture. Cook for about 10 to 15 minutes, then stir in the salt, tomatoes, fresh coriander and garam masala .