1) Preheat the oven to 350°F, and grease two baking sheets, or line with parchment paper.
2) To make the cookies: Beat together the butter, sugar, salt, and Fiori until creamy.
3) Add the flour, and mix just until incorporated.
4) Shape teaspoon-sized balls of dough, and roll them in sparkling sugar.
5) Place the cookies 1" apart on the prepared baking sheets.
6) Bake the cookies until they're just beginning to brown along the edges, 16 to 18 minutes. Remove from the oven, and cool completely.
7) To make the filling: Beat all the ingredients together until light and fluffy.
8) To assemble the cookies: Sandwich a 1/4"-thick layer of filling between two cookies, and roll the filling edge in the colored sugar or sprinkles.
Yield: 24 to 26 filled cookies.