In a mixing bowl, cream butter and sugar until fluffy. Add egg yolk; mix well. Add flour just until blended (mixture will be crumbly). Press onto bottom and up sides of an ungreased 9-inch tart pan with removeable bottom. Bake at 375° for 12-14 minutes. Cool in the pan on a wire rack. Sprinkle nuts over crust. In a heavy saucepan, combine sugar, butter, corn syrup and 2 tbsp of cream. Boil and stir over medium heat for 1 minute. Pour over walnuts. Bake at 375° for 10-12 minutes or until bubbly. Cool. Beat remaining cream until stiff. Serve tart at room temperature with whipped cream.