Line a 9×13-inch baking pan with foil, leaving extra over the edges. Grease the foil with 1 tablespoon of butter.
In a large heatproof bowl, add broken milk chocolate bars, semisweet chocolate chips, marshmallow creme, and chopped walnuts. Set aside.
In a saucepan, combine evaporated milk, sugar, and remaining 8 tablespoons of butter. Cook over medium-low, stirring constantly. Bring to a boil and let it bubble for 4 minutes.
Pour the hot sugar mixture over the chocolate bowl. Stir immediately until melted, smooth, and fully combined.
Transfer the mixture to the prepared pan. Spread it evenly with the back of a spoon or spatula.
Cover and refrigerate for at least 2 hours, or until the fudge is firm to the touch.
Lift out the fudge using the foil. Cut into 1-inch squares and store in an airtight container in the fridge for up to 3 weeks.