Line two baking sheets with wax paper. Beat the butter, brown sugar, and vanilla extract until well combined. Slowly mix in the flour until just combined. Using a wooden spoon, stir in the miniature chocolate pieces.
Shape the dough into 3/4" to 1" (2 cm to 2.5 cm) balls and place them on the first baking sheet. Freeze for 30 minutes or until firm.
While the cookie dough is in the freezer, use a clean, dry saucepan to heat the chopped chocolate, candy coating, and shortening over low heat. Stir until the chocolate is melted and smooth, then remove from heat.
Using two forks, roll or dip each ball in the chocolate mixture, one at a time. Allow the excess chocolate to drip back into the saucepan before placing the truffles on the second lined baking sheet. Decorate with sprinkles and chill for 20-30 minutes. Drizzle the truffles lightly with any remaining melted chocolate mixture.
Store in an airtight container in the refrigerator.
Notes
Make sure all the tools used for melting the chocolate are dry. Even a tiny water droplet will make the chocolate seized (harden) when it is melting. You can also use the double boiler or microwave method to melt the chocolate.