In a mixing bowl, cream the butter and brown sugar until light and fluffy. Add the flour, sweetened condensed milk and vanilla; mix well. Stir in the chocolate chips and walnuts, if using.
Shape into 1-inch balls; place on waxed paper-lined baking sheets. Loosely cover and freeze for 1-2 hours or until firm. (The dough softens quickly at room temperature so it works best if they are frozen, not just chilled in the refrigerator.)
In a microwave safe bowl, melt candy coating, stirring often until smooth. Dip balls in coating; place on waxed paper-lined baking sheets.
Refrigerate until firm, about 15 minutes. If desired, melt remaining candy coating and drizzle over candies. Store in refrigerator.