Line an 8×8-inch square baking pan with parchment paper, leaving an overhang on the sides. This makes it easy to lift the fudge out once it has set. Lightly grease the parchment with a tiny bit of butter or non-stick spray for easy release.
In a large heavy-bottomed saucepan over medium-low heat, combine the white chocolate chips, sweetened condensed milk, and butter. Stir constantly with a silicone spatula until the mixture is completely smooth and melted. Be careful not to let the mixture boil or scorch.
Once the mixture is smooth, remove the pan from the heat. Stir in the pure maple syrup, maple extract, vanilla extract, and salt. Mix thoroughly until the liquids are fully incorporated and the mixture looks glossy.
Gently fold in 1 cup of the chopped walnuts. Ensure they are evenly distributed throughout the fudge mixture so every bite has a bit of crunch.
Pour the mixture into the prepared baking pan and spread it evenly with a spatula. Sprinkle the remaining 1/2 cup of walnuts over the top, pressing them down lightly so they stick. Let the fudge cool to room temperature, then refrigerate for at least 3 hours or until firm.
Once the fudge is fully set, lift it out of the pan using the parchment paper overhang. Use a sharp knife to cut the fudge into small squares. For the cleanest cuts, wipe the knife with a warm, damp cloth between each slice.