In a stand mixer bowl, cream butter and sugar until light and fluffy.
Beat in egg yolk and mix again.
Gradually add flour just until blended (mixture will be crumbly).
Press onto the bottom and up the sides of an ungreased 9-in. tart pan with removable bottom. Place pan on baking sheet. Bake at 375° for 12-14 minutes. Cool in the pan on a wire rack. Leave the oven on.
Walnut Filling
Spread the walnut in a baking sheet. Bake in the oven for 5 minutes to draw it’s natural oils. Sprinkle nuts over crust.
In a small heavy saucepan, combine sugar, butter, corn syrup and 2 tablespoons of cream. Boil and stir over medium heat for 1 minute longer. Pour over walnuts.
Bake for 10-12 minutes or until bubbly. Cool on a wire rack.