Roast the Jalapeños: Place the diced jalapeños in a dry cast iron skillet over medium heat. Cook them, rolling them around the pan occasionally, until the outsides begin to cook and darken slightly.
Make the Base: Transfer the roasted jalapeños to a blender. Add the green onions, cilantro, and half of the corn. Blend until the mixture is chunky.
Simmer: Reduce the heat in the skillet. Return the chunky corn mixture to the pan. Add the remaining corn, heavy cream, salt, and pepper.
Thicken and Finish: Simmer the mixture for about 20 minutes, or until it has slightly thickened. Stir in the butter and adjust the seasoning with additional salt and pepper to taste before serving.