In a large mixing bowl, add the room-temperature butter, chocolate chips, and vanilla. Save the butter wrapper to butter a 7x11-inch baking dish then snugly fit with a piece of parchment paper, allowing enough parchment to fall over the long sides of the pan, like a sling, and set aside.

In a non-stick electric frying pan, stir together the sugar and the evaporated milk until smooth. Add the marshmallows and set the frying pan to 250°F.

Cook and stir constantly with a rubber spatula, cleaning the sides of the pan as the marshmallows begin to melt. Once the marshmallows have melted, continue to cook and stir until the sugar has melted and the mixture turns a tawny tan, about 5 minutes.

Turn off the heat and pour the hot mixture over the butter and chocolate chips in the bowl. Working quickly, use a wooden spoon to stir the butter and chocolate until they melt and combine. Add the nuts, then vigorously stir the mixture until glossy, about 2 minutes.

Transfer the chocolate mixture to the baking dish and smooth the top with an angled offset spatula. Cover with plastic wrap and refrigerate for 3 hours or overnight.

To serve, let the fudge sit for 1-2 minutes after removing it from the fridge, and use the parchment paper to lift the fudge from the pan to a cutting board. Cut, and serve.