Bring the stock to a boil in a deep skillet. Sprinkle the chicken breasts with salt and pepper and add to broth. Cover and cook 8-10 minutes, or until cooked through then lift out the chicken, reserving the stock, wrap in a damp towel and set aside to cool.
Heat 2 tablespoons of vegetable oil in a stockpot over medium heat. Saute the onions with 1 teaspoon salt and 1/2 teaspoon pepper until soft. Add garlic and cook 2-3 more minutes, do not brown. Add red salsa, reserved chicken stock and water and bring to a boil, then reduce to a simmer and cook 10 minutes.
Shred the chicken meat into long thin strips and add to the pot along with the corn chips. Taste and adjust salt and pepper depending on how salty the chips are. Continue simmering 3-4 minutes then serve immediately while chips are still half crispy with garnishes on top.
Heat the vegetable oil in a medium skillet over moderate heat. Cook the onions until soft, about 10 minutes. Transfer to a food processor fitted with the metal blade or a blender.
Add the remaining ingredients, except the salt and puree, in batches if you are using a blender, until smooth. Pass through a medium strainer, pressing with a spatula or wooden spoon to push through as much pulp as possible. Pour into a saucepan, and add the salt. Bring to a boil, reduce to a simmer and cook, uncovered, 20 minutes. Adjust the seasonings. Set aside to cool for table salsa or use warm for red rice or chilaquiles. Store in refrigerator 2 to 3 days or in the freezer for weeks
In a large bowl whisk together cream and buttermilk. Cover and set in a warm place (a gas oven with just the heat from the pilot light for example) for 8 hours. Place in refrigerator. Can be kept for up to a week.