Line a 9x13inch baking pan with parchment paper.
Add the butter, sugar, and evaporated milk to a large heavy saucepan over medium heat.
Stir the mixture occasionally as it comes to a boil. Once boiling stir constantly, and then heat until it reaches a temperature of 234 F (this will take about 5 minutes)
Remove the mixture from the heat, and add in the white chocolate chips and marshmallow creme. Stir the mixture until the chocolate chips are melted and everything is stirred well together.
Add in the maple extract and salt and stir it into the mixture.
Fold in the chopped walnuts until they are spread evenly through the mixture.
Pour the mixture into the prepared pan and spread the top smoothly. Sprinkle it with additional walnuts, and flaky sea salt if desired.
Cover the fudge and place it in the fridge to chill for at least 2 to 3 hours.
Slice it up and serve.