In a large pot, bring 3 quarts of water to a rolling boil.
Peel or scrub the potatoes. Carefully add to the boiling water. Add the salt.
Boil until soft but not too soft. We don't want them to fall apart when we mix in the dressing. 15-20 minutes should do it for small-medium sized potatoes.
Drain and set aside to cool.
After they have cooled, cut into small bitesized pieces, about a 1/2 dice, and place in a large bowl.
In another bowl mix the sour cream, mayo, diced jalapenos, green onions and cilantro if using. (If you prefer, add the dressing ingredients to your food processor and pulse until smooth.).
Pour dressing over the potatoes and gently toss to coat. (actually, I've found that after the intial toss, putting a tight fitting lid on the bowl and inverting it a couple of times mixes the salad pretty well without breaking up the potatoes.).
Garnish with parsley and/or cilanto and/or grape tomatoes.