Begin by melting 1.5 tablespoons of unsalted butter in a skillet over medium heat. Once the butter is bubbling, add 1.5 cups of pecan halves, toasting them for about 4-5 minutes. Stir frequently until the pecans are lightly browned and fragrant. Remove the skillet from heat and set the pecans aside, allowing them to cool.

Next, line an 8x8 inch pan with parchment paper and lightly grease it. In a medium saucepan over medium-low heat, brown 3 tablespoons of unsalted butter, stirring constantly until it turns golden brown and emits a nutty aroma—this should take about 3-5 minutes. Remove it from heat to prevent burning.

In a heatproof bowl set over a saucepan of simmering water, combine the sweetened condensed milk, 20 ounces of chopped white chocolate, and the browned butter. Stir gently until the mixture is completely melted and smooth, which should take about 5-7 minutes. Remove it from heat and let it cool slightly.

Once the fudge mixture has cooled, whisk in 1 teaspoon of vanilla extract, 1/8 teaspoon of salt, and 1.5 teaspoons of ground cinnamon. Then, fold the toasted pecans into the mixture until they're evenly distributed.

Pour the fudge mixture into the prepared pan, using a spatula to spread it evenly. For an extra touch, sprinkle a pinch of sea salt on top if desired. Cover the pan with plastic wrap and refrigerate for at least 2 hours, or until the fudge is firm and set.

Once chilled, remove the fudge from the refrigerator and lift it out of the pan using the parchment paper. Cut it into small squares and serve cold. Store any leftovers in an airtight container in the fridge for up to a month.