2 - 3 bunches of fresh mustard greens
1 - 2 bunches fresh spinach, OR 1 block of frozen spinach
1 small onion, chopped (about 1/2 - 3/4 cup)
2 cloves garlic
1/2 - 1 tsp. powdered ginger, OR a little bit of chopped fresh ginger (to taste)
small, hot green chili pepper (optional)
1/2 - 1 tsp salt (to taste)
1 - 1 1/2 tsp chili powder or cayenne pepper (to taste)
approx 1/4 cup butter, or butter and vegetable oil
handful corn flour

Wash greens thoroughly in plenty of water.  Remove and throw away big stems and any rotten or badly damaged leaves.  Tear or chop crosswise into about 2 inch long pieces.  Place in a large pot and fill about half-way with water.  Cover and simmer for about 2 hours until very soft and only a little bit of water left in the bottom.  If using frozen spinach, add about half-way through.

Fry chopped onion, garlic (and opt. fresh chopped ginger and green hot pepper) in butter, or oil and butter mixture, until onion is brown, or \'carmelized\'.  Stir in salt, chili powder, and powdered ginger and add to greens while cooking, when nearly done.

When greens are very soft and tender and there is only a little liquid left, remove from heat.  Blend mixture in blender (do in 2 batches, half at a time) and then place back on low heat.  (You can also use an electric hand mixer, but be sure to chop your greens a little smaller if you do so). 

Sprinkle a handful of corn flour over the top while stirring, and then stir really well to prevent corn flour lumps.  The corn flour will thicken the saag.  Continue to heat over low heat for a little while, stirring occasionally - maybe 5 or 10 minutes.  Add a little more corn flour, if needed.  Don\'t let it scorch.  Remove from heat. 

Serve Saag with regular or whole wheat roti/chappati, or corn roti (Makki Roti). 
Some people also like to eat their Saag with a chunk of butter melting on top.