2. Place bittersweet chocolate, semisweet chocolate, and sweetened condensed milk in a bowl set over a pan of simmering water, making sure that the water is not boiling and that the bowl is not touching the water.
3. Stir the mixture occasionally until the chocolate has melted. Stir in the vanilla extract and nuts.
4. Spread fudge evenly in prepared baking pan. Refrigerate for 2 hours, or until firm. Cut when cool and firm.
Storing: Fudge generally should not be stored in the refrigerator because it can dry out. It can be stored for up to a week in an airtight container at room temperature. If you wish to store it for longer than a week, fudge can be frozen for up to six months. Wrap in wax paper and place in a freezer bag.