Old Fashioned Christmas Brown Sugar Fudge

Butter the inside of an 8 inch square baking pan. Lightly butter the inside of a large saucepan. Combine sugar, cream, brown sugar and corn syrup in the prepared saucepan. Cook, stirring, over medium heat until mixture reaches 238 degrees on a candy thermometer. Remove the pan from the heat. Sprinkle the diced butter over the top of the brown sugar mixture. Let stand 10 minutes. Add white chocolate chips and walnuts. Stir until chocolate is melted. Spread the mixture evenly in the prepared baking pan. Refrigerate fudge until firm. Cut fudge into squares. Store fudge, refrigerated, in an airtight container.