Pit the avocado by cutting it lengthwise around the seed and then twisting the two halves apart to expose the pit. Remove the pit and use a tablespoon to scoop the avocado flesh out of the skin and into a food processor. Add the mayonnaise, ranch dressing mix, buttermilk, shallot, garlic, cilantro, lime juice, and jalapenos. Give it a whirl until everything it blended smooth. Taste and adjust seasonings.