For crust, in a large bowl, mix flour, sugar and salt; cut in butter until crumbly. Gradually add ice water, tossing with a fork until dough holds together when pressed. Shape into a disk; wrap in plastic wrap. Refrigerate 1 hour or overnight.

For toffee, grease a 15x10x1-in. pan with 1/2 teaspoon butter. In a large heavy saucepan, combine sugar, salt and remaining butter. Cook over medium heat until a candy thermometer reads 300° (hard-crack stage), stirring constantly. Remove from heat. Stir in walnuts, cooked bacon and vanilla. Immediately pour into prepared pan. Let stand until set, about 45 minutes. Coarsely chop enough toffee to measure 4 cups; set aside. Break the remaining toffee into pieces; refrigerate to serve with pie or save for another use.

On a lightly floured surface, roll pastry dough to a 1/8-in.-thick circle; transfer to a 9-in. deep-dish pie plate. Trim pastry to 1/2 in. beyond rim of plate; flute edge. Refrigerate 30 minutes. Preheat oven to 425°.

Line pastry with a double thickness of foil. Fill with pie weights, dried beans or uncooked rice. Bake on a lower oven rack 20-25 minutes or until edges are golden brown. Remove foil and weights; bake 3-6 minutes longer or until bottom is golden brown. Cool on a wire rack.

For filling, place egg yolks in a small bowl; let stand at room temperature 30 minutes. In a large heavy saucepan, mix brown sugar, flour and salt. Whisk in milk. Cook and stir over medium heat until thickened and bubbly. Reduce heat to low; cook and stir 4 minutes longer. Remove from heat.

Gradually whisk a small amount of hot mixture into egg yolks; return all to pan, whisking constantly. Bring to a gentle boil; cook and stir 2 minutes. Immediately transfer to a clean bowl; stir in butter and vanilla until smooth.

Place 3 cups of the chopped toffee into crust; pour filling over toffee. Top with remaining 1 cup chopped toffee. Refrigerate, covered, at least 2 hours before serving. Serve with whipped cream and remaining toffee pieces. Yield: 12 servings plus 1 pound toffee.