Pumpkin Walnut Fudge

4 cups sugar
1 cup milk
3 tablespoons light corn syrup
1 cup pumpkin puree
3 tablespoons unsalted butter, cut into bits
1 teaspoon vanilla
2 cups chopped walnuts

In a 4 quart heavy saucepan combine sugar, milk, corn syrup, pumpkin and a pinch of salt. Cook the mixture over med. heat, stirring, until sugar dissolves and cook it undisturbed, until a candy thermometer registers 238ºF. Remove the pan from heat, add butter (do not stir it into mixture), and let the mixture cool until it is 140ºF. Stir in vanilla and walnuts. Beat the mixture with a wooden spoon for 30 sec-1 min. , or until it begins to lose its gloss. Pour immediately into a buttered 9" square pan. Let the fudge cool until it begins to harden. Cut it into squares. Let it cool completely.