Saag and palak are intensely green Indian curries, containing greens, onion, ginger and tumeric. The two dishes may sometimes be served interchangeably in restaurants, but do contain different spices and dairy ingredients. Palak is actually a type of saag – the word for green leafy vegetables in Hindi.
Saag refers to all leafy green vegetables; a true saag curry, sometimes called saagwala, includes mustard greens and fenugreek leaves as well as spinach leaves. Palak is the Hindi word for spinach. Thus, the only greens in a palak curry are mature spinach leaves.
Dozens of recipes for saag and palak curries exist; the slight variations are determined by family tradition and cooks' preferences. Saag generally contains a blend of spices known as garam masala, which usually contains coriander, ginger, cardamom and black peppercorns. Garlic also has a big presence in this heady curry. Palak curry relies on cumin, fennel and coriander for flavor, with a bit of cayenne and red chiles for heat. Garlic is noticeably absent from authentic palak curries.
Saag curry tends to be richer and creamier, due to the addition of heavy whipping cream at the end of the cooking process. Palak curry uses yogurt, instead of cream, as the dairy ingredient. This results in a drier sauce that has a distinct tanginess. The yogurt gets stirred in at the end of the cooking process too, but it can curdle when warmed, so chefs often stir a small amount of cream into the yogurt before adding it to the curry to prevent the curdling without adding too much milky flavor to the palak.
Palak and saag curries are often served with paneer, or Indian cheese. Cubes of of this bland cheese, made by cooking milk with lemon juice, can be stirred into the pureed sauces to create a vegetarian entrée that's traditionally served over rice. Restaurants sometimes serve saag curry mixed with cubes of cooked chicken or lamb, too.