Lightly butter a 6-cup baking pan (square or rectangular) or a platter. Set aside. Combine the chocolate with the nuts, butter and vanilla in a large heatproof mixing bowl. Set aside.

Combine the marshmallows and sugar in a heavy-bottomed stockpot. Stir in the evaporated milk and place over medium heat. Stirring constantly, bring to a boil. Continuing to stir, boil for 6 minutes.

Remove mixture from the heat and pour the hot marshmallow mixture into the chocolate mixture. Beat vigorously until the fudge is creamy. Scrape the fudge into the prepared pan or platter. Spread the fudge evenly with the back of a spoon.

Cool at least 1 hour before cutting into small squares. Store, in layers seperate a by wax paper, for up to 1 week or, refrigerated, for up to 3 weeks. Bring to room temperature before serving.