Bittersweet Truffles

Directions

1. 1
   Melt butter in a heavy saucepan over low heat; stir in 3/4 cup cocoa.
2. 2
   Gradually add condensed milk, stirring constantly, until smooth.
3. 3
   Cook over medium heat, stirring constantly, until thickened and smooth (about 3 minutes).
4. 4
   Remove from heat; stir in vanilla.
5. 5
   Pour mixture into a lightly greased 8-inch square pan. Cover mixture and chill at least 2 hours and cut into squares.