1. Beat butter, brown sugar, egg and vanilla in large bowl until blended. Stir together flour, cocoa, baking powder and baking soda; add with milk to butter mixture until well blended. Stir in nuts and toffee bits.
2. Refrigerate until firm enough to handle, at least 2 hours. Heat oven to 350°F. Line cookie sheet with parchment paper or lightly grease. Remove wrappers from chocolates. Shape dough into 1-inch balls. Press chocolate piece into each ball, covering completely with dough. Reshape into balls; place on prepared cookie sheet.
3. Bake 8 to 10 minutes or until set. Cool slightly; remove from cookie sheet to wire rack. Cool completely; roll in powdered sugar. Makes about 5 dozen cookies.