1½lb.semisweet or milk chocolatecoarsely chopped (Baker's chocolate)
Mini chocolate chipsfor garnish
Combine the butter and sugar in a mixing bowl and cream on medium-high speed until light and fluffy, about 2 minutes. Beat in the flour, sweetened condensed milk and vanilla until incorporated and smooth. Stir in the chocolate chips. Cover with plastic wrap and refrigerate until the mixture has firmed up enough to form balls.
Shape the chilled cookie dough mixture into 1-1½ inch balls. Place on a baking sheet lined with wax paper. Cover loosely, transfer the pan to the freezer and chill for 1-2 hours.
When ready to dip the truffles, melt the chopped chocolate in a heatproof bowl set over a pot of simmering water. Dip each chilled truffle, one at a time using a fork, coating in chocolate and shaking gently or tapping against the bowl to remove the excess. (If at any point during dipping, the cookie dough balls become too soft, return to the freezer to chill for 30 minutes.) Transfer to a wax-paper lined surface. If using mini chocolate chips for garnish, sprinkle on top quickly after dipping each truffle before the chocolate sets. Once all the truffles have been dipped, store them in the refrigerator until ready to serve.