Line an 8x8-inch square baking pan with parchment paper, leaving a 2-inch overhang on two sides. Set aside.

In a large microwave-safe bowl, combine white chocolate chips, sweetened condensed milk, butter, and salt. Microwave in 30-second intervals, stirring between each, until completely melted and smooth (about 2-3 minutes total).

Split vanilla beans lengthwise and scrape out all the seeds using the back of a knife. Add vanilla seeds to the melted chocolate mixture along with the vanilla extract.

Add marshmallow cream to the bowl and beat with a wooden spoon for 2-3 minutes until fully incorporated and the mixture is glossy and smooth.

Pour the fudge mixture into the prepared pan, spreading it evenly with a spatula. Tap the pan gently on the counter 2-3 times to release any air bubbles.

Let the fudge set at room temperature for 1 hour, then transfer to the refrigerator to firm up completely for at least 2 hours or overnight.

Using the parchment overhang, lift the fudge out of the pan onto a cutting board. Use a sharp knife to cut into 36 squares (6x6 grid), wiping the knife clean between cuts for neat edges.