Line a 9x13-inch pan with parchment paper.

In a large saucepan over medium heat, mix the sugar, butter, and evaporated milk.

Bring the mixture to a boil and leave on heat until the mixture registers 234°F on a candy thermometer (about 5 minutes).

Remove from heat and stir in chocolate chips until melted and thoroughly combined.

Add the mini-marshmallows, walnuts, and vanilla extract, and stir to incorporate.

Transfer the fudge to the prepared pan and allow to set at room temperature (about 4 hours) or chill in the refrigerator to speed up the process.

Serve at room temperature.