Beat sugar, butter, and vanilla on medium speed until creamy. Reduce speed to low, add flour and 1/2 cup of toffee bits and beat until well mixed.
Shape dough into 1 inch balls, Roll each ball into 2 1/2 inch rope with tapered ends; curve slightly into crescent shape. Place 1 inch apart onto ungreased cookie sheets. Bake at 325 for 11-16 minutes or until set and very light brown.
Place chocolate chips and shortening in small microwave safe bowl. Melt on high for 1 minute; stir. Continue melting in 30 second intervals until almost melted. Stir until smooth.
Dip one end of the cooled crescent in the chocolate. Sprinkle with additional toffee bits.
Place on wax paper until chocolate is set. (About 1 hour). Sprinkle with powdered sugar if desired.