1Heat oven to 400°F. Grease cookie sheet with shortening or cooking spray, or line with cooking parchment paper or silicone baking mats.
2In large bowl, beat granulated sugar, 1/2 cup butter, the buttermilk, vanilla, egg and chocolate with electric mixer on medium speed, or mix, until well blended. Stir in flour, baking soda and salt. On cookie sheets, drop dough by rounded tablespoonfuls about 2 inches apart.
3Bake 8 to 10 minutes or until almost no indentation remains when touched in center. Immediately remove from cookie sheet to cooling rack. Cool completely, about 30 minutes.
4In large bowl, beat all filling ingredients on medium speed about 2 minutes or until light and fluffy. Place flat sides of 2 cookies together with scant 3 tablespoons filling, sandwich-style. Sprinkle edges of filling with crushed candies. Store in tightly covered container.