In a microwave-safe bowl, combine white chocolate chips, sweetened condensed milk, and maple syrup. Microwave on high for 90 seconds. Stir until smooth.
Add salt and butter. Mix until smooth. If using walnuts, stir into fudge until combined.
Pour into a buttered 8-inch square pan.
Refrigerate until cool. Cut into 1-inch squares and store in an airtight container.
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