Preheat the oven to 375°F. Have two ungreased cookie sheets on hand., In a large bowl, mix together the butter, sugar, cream cheese, salt, vanilla, Fiori di Sicilia, and zest just until smooth. Beat in the egg yolk, then mix in the flour., Fill a cookie press 3/4 full with the dough and press the cookies onto the baking sheets. Give the press a quarter turn after squeezing and before lifting it up; this can help the cookies stay in place. Sprinkle with sparkling sugar., Bake the cookies for 9 to 11 minutes, until light brown around the edges., Remove the cookies from the oven and cool on the pan on a rack for 5 minutes. Transfer cookies from the pan to the rack to finish cooling completely., Store cooled cookies, well-wrapped, at room temperature for several days; freeze for longer storage.