Cream butter and 1/2 cup confectioners’ sugar at with mixer at medium speed until light in color, about 1 minute. Hand stir in cake flour, vanilla, salt until well blended. Stir in pecans.
Loosely cover dough with plastic wrap and refrigerate until firm, about 1 hour.
Position racks in center and top of oven. Preheat oven to 350
Completely enclose each Frango mint half in about 1 level tablespoon of dough. Roll in your palms to form a ball.
Place cookies 1” apart on ungreased baking sheets. Bake 18-20 minutes, switching the position of the sheets at about 10 minutes.
Remove the slightly golden cookies from the oven. Sift (or not) the confectioners’ sugar into a bowl and roll the warm cookies in it. Cool. Roll them a second time when they are cool