For a spicier dish, leave some of the serrano pepper seeds in. To mellow the heat, be sure to remove all seeds and ribs. If you don't have creme fraiche, sour cream can be substituted. However, the flavor will be slightly tangier. Freshly shucked corn is best for this recipe, but frozen corn can be used in a pinch. Be sure to thaw it completely before adding it to the pan. The roasted red pepper can be made ahead of time, or purchased pre-roasted from the store.