Peel and cut up potatoes into big chunks, 1" x 1" x 1".
Cut up beef and onion into the same size. You can substitute chicken or lamb for beef, if you like.
Heat coconut milk and masaman curry paste in a pot over medium to low heat and stir. Break up the paste and mix well with coconut milk. Stir constantly to keep the mixture from sticking.
When you see the red oil bubbling up (about 5 minutes), add the meat and stir to cover the meat with curry. Add half a cup of water or enough to cover all the meat.
Add the rest of the ingredients, except for potatoes, onions and peanuts.
Stew for 1/2 hour or until beef is getting tender.
Add potatoes, onions and peanuts.
Let simmer for 20 minutes more. The liquid should be reduced and you should be able to see some chunks. But, if the liquid is very low, add more water.
Serve hot with "Cold Cucumber in Vinegar", which is: 1/3 cup water, 1/3 cup vinegar, 1/4 cup sugar, 2 shallots (thinly sliced), 1 cucumber (quartered and thinly sliced), 1 long hot pepper (sliced), all tossed together, and chilled.
However, if you're not up for making this quick little salad, just serve over rice, or eat it by itself.