Prepare pan:
Butter a 9-by-13-inch baking dish pan, or mist it in with nonstick cooking spray.

Mix ingredients:
Stir together the semisweet chocolate, German's chocolate, and marshmallow cream in a large bowl.

Boil sugar and milk:
Bring the sugar, salt, butter, and evaporated milk to a boil in a medium saucepan over medium-high heat. Boil for 1 minute. Reduce the heat and simmer 7 minutes, stirring continuously.
Pour the hot syrup over the chocolate mixture and stir until smooth.
Stir in the nuts.

Add to pan:
Pour into the prepared pan. Let stand undisturbed at room temperature until firm, preferably overnight.

Slice and serve:
Cut the fudge into small squares. Store in an airtight container for up to two weeks. Some people prefer the texture of this fudge when it is chilled after it is cut.