Line a 9×13-inch baking pan with foil, making sure it overhangs the edges so you can lift the fudge out later. Grease the foil with 1 tablespoon of the butter to prevent sticking.

In a large heatproof mixing bowl, add the broken milk chocolate candy bars, semisweet chocolate chips, marshmallow creme, and chopped walnuts. Having these ready ensures the hot syrup can melt and incorporate everything smoothly.

In a medium saucepan, combine the evaporated milk, granulated sugar, and the remaining 8 tablespoons of butter. Place over medium-low heat and stir frequently as the butter melts and sugar dissolves.

Once the mixture reaches a boil, continue boiling for exactly 4 minutes, stirring constantly. This step is crucial for achieving the perfect texture—boiling too little can make the fudge too soft, and boiling too long can make it grainy.

Carefully pour the hot milk and sugar mixture over the chocolate mixture in your large bowl. Stir vigorously until the chocolate is fully melted and the mixture is smooth and glossy.

Transfer the fudge mixture into your prepared pan. Use the back of a spoon or an offset spatula to spread it evenly. Cover and refrigerate for about 2 hours, or until firm.

Once the fudge has set, lift it out of the pan using the foil overhang. Peel away the foil and cut the fudge into 1-inch squares. Store in an airtight container in the refrigerator for up to 3 weeks.