Line an 8x8-inch square baking pan with parchment paper, leaving a 2-inch overhang on two opposite sides for easy removal later.

Add the white chocolate chips to a large microwave-safe bowl. Microwave at 50% power in 30-second intervals, stirring thoroughly between each burst, until the chocolate is melted and smooth — this should take 2-3 minutes total.

Pour the sweetened condensed milk over the melted white chocolate immediately while still warm. Add the vanilla extract and salt.

Stir gently with a rubber spatula until the mixture is completely smooth and uniform in color, about 1 minute. Avoid overmixing once combined.

Pour the fudge mixture into the prepared pan and spread evenly with an offset spatula or the back of a spoon. Tap the pan gently on the counter 2-3 times to release any air bubbles.

Let the fudge sit uncovered at room temperature for 30 minutes, then transfer to the refrigerator to set completely for at least 2 hours.

Once firm, use the parchment overhang to lift the fudge out of the pan. Place on a cutting board and use a sharp knife (wiped clean between cuts) to slice into 36 small squares.

Serve at room temperature for the creamiest texture. Store in an airtight container with parchment paper between layers.