Roast. Preheat the oven to 425°F. Coat the jalapeños with oil, sprinkle with a little salt, and place on a sheet pan. Roast in the oven for 15 minutes, turning about half way through. The jalapeños can also be roasted in a toaster oven without the need to preheat for the same time and temperature.
Dice. Let the peppers cool enough to handle. On a cutting board remove the tops and slice in half. Spread the peppers flat and scrape out the seeds and the white 'ribbing' inside. The spicier you want it, leave more of the white ribbing and a few seeds. Give the jalapeños a rough chop.
Blend. Remove the avocado from the skin and discard the pit. Place the jalapeños, avocado, pineapple juice, sour cream and salt to a blender or food processor. Blend on high until fully puréed, smooth and creamy.
Notes
For a thinner consistency, add pineapple or lime juice 1 tablespoon at a time.
Jalapeño avocado crema will keep for up to 3 days refrigerated. You may need to scrape the thin layer of oxidized avocado from the top before serving.