Tangy feta makes this flavorful dip great as a spread for a grilled-vegetable sandwich, too.
Puree feta, hearts of palm, salt, oil, and 1 tablespoon water in a food processor until smooth, about 3 minutes. Add dill; pulse just to combine.
Transfer to a serving bowl, cover, and refrigerate until cold, at least 30 minutes and up to 1 day. Sprinkle with cayenne and more dill; serve, with crostini.