Melt the margarine in a large pot and saute the chopped onions on medium heat.
While theyre sauteing, start peeling, cutting up your potatoes.
Once the onions have turned clear, add the potatoes, chicken broth, and cumin.
Stir and bring to a boil.
Then cover, reduce heat to medium, and allow the potatoes to cook until they soften enough to eat (about 20 minutes).
After the potatoes have cooked, remove the pot from the heat and add the chopped jalapeno, a pinch of baking soda, and the evaporated milk.
Mash the potatoes with a potato masher (or a large fork if you dont have a potato masher) while theyre still in the pot.
Stir thoroughly and add the salt and pepper.
Simmer for 15 minutes, stirring often.
Note that 2 tablespoons of jalapeno is spicy.
Adjust more or less to your taste.
I have used both fresh and canned jalapenos; fresh does give a better flavor, but canned works perfectly fine.
I do think canned gives a bit more spice though!