Place chocolate in large bowl and place over pan of simmering water. Do not allow bowl to touch water (or, use double boiler). Heat until chocolate melts and is smooth and silky, stirring frequently. Meanwhile, in a very small pan heat condensed milk and butter until butter melts. Add this mixture to melted chocolate and stir until smooth. Stir in the cheese spread. Place bowl back over simmering water if necessary to incorporate until mixture is smooth. Refrigerate 3 hours or overnight.
Working quickly, roll the refrigerated mixture into smooth 1-inch balls (the mixture is stiff; it may have to sit at room temperature until it's pliable.) Place on parchment or waxed paper. Roll the truffles in the cocoa powder. Refrigerate and bring to room temperature at serving time. Refrigerate any remaining truffles.
Coating option in place of cocoa powder: Melt 6 ounces best quality dark or semisweet chocolate in bowl over pan of simmering water. Roll the truffle balls in the chocolate to evenly coat.