Either by hand or with an electric mixer, cream the butter, the 1 cup sugar and the brown sugar at medium speed until light and fluffy, about 3 minutes, scraping down the sides of the bowl with a rubber spatula, as needed. Add the egg and Fiori di Sicilia; beat at medium speed until combined, about 30 seconds. Add the dry ingredients and beat at low speed until just combined, about 30 seconds, scraping down the bowl as needed.