1. Line an 8×8 inch baking pan with parchment paper, leaving an overhang on two sides, and lightly mist with nonstick spray.

2. Add the unsalted butter to a light-colored saucepan over medium heat. Melt, then cook, stirring often, until the butter foams and the milk solids turn golden brown and smell nutty. Remove from heat as soon as it reaches a deep amber color.

3. Stir in the sweetened condensed milk until the mixture is smooth and fully combined with the brown butter.

4. Return the pan to low heat and add the white chocolate chips. Stir constantly until the chips are completely melted and the mixture is thick, glossy, and smooth.

5. Remove from the heat. Sift in the powdered sugar and stir vigorously until no lumps remain. Add the vanilla extract and fine sea salt and mix until everything is evenly incorporated.

6. Pour the warm fudge mixture into the prepared pan, scraping the saucepan well. Smooth the top into an even layer and gently tap the pan on the counter to release air bubbles.

7. Refrigerate for at least 2 hours, or until firm. For best texture and clean slices, chill overnight.

8. Use the parchment overhang to lift the fudge from the pan onto a cutting board. Cut into about 36 small squares and serve slightly chilled or at cool room temperature.