1 1/2 c. graham cracker crumbs
6 tbsp. unsalted butter, melted
1/4 c. firmly packed dark brown sugar

Preheat oven to 350 degrees. Lightly butter inside of 9-inch diameter springform pan with 2 3/4-inch high-sides. Combine crumbs, butter, brown sugar in small bowl. Press crumbs over bottom and 1 inch up sides of pan. Refrigerate crust.

FILLING:

2 lbs. cream cheese, room temperature
1 1/2 c. sugar
5 lg. eggs, room temperature
2 1/2 tsp. vanilla extract
2 tsp. fresh lemon juice

Using electric mixer, beat cream cheese in large bowl until fluffy. Add sugar and beat until smooth. Beat in eggs 1 at a time. Mix in vanilla extract and lemon juice.

Pour filling into prepared crust. Bake until cake rises about 1/2 inch over rim and center moves only slightly when pan is shaken, about 1 hour and 15 minutes. Cool on rack. (Cake will fall as it cools, sinking in center.) Cover and refrigerate until well chilled, at least 6 hours. (Can be made 1 day ahead.)

TOPPING:

1 1/4 c. sugar
1/3 c. water
1 c. whipping cream
1/2 c. unsalted butter, cut into sm. pieces, room temperature (1 stick)
1 tsp. vanilla extract
3/4 c. whipping cream
2 tbsp. sugar
3 (1.4 oz.) toffee candy bars (such as Skor), broken into pieces

Heat sugar and water in heavy saucepan over low heat, stirring until sugar dissolves. Increase heat and boil without stirring until mixture is rich caramel color, occasionally swirling and washing down sides of pan with brush dipped in cold water, about 8 minutes. Reduce heat to very low. Add cream (mixture will bubble up) and stir until smooth. Mix in butter. Cool slightly. Mix in vanilla.

Using small sharp knife, cut around sides of pan to loosen cake. Release pan sides. Pour 2/3 cup caramel sauce into center of cake. Cover remaining caramel sauce and let stand at room temperature. Chill cake until caramel topping is almost set, about 2 hours. (Can be prepared 8 hours ahead.)

Whip 3/4 cup cream with 2 tablespoons sugar in medium bowl until firm peaks form. Spoon cream into pastry bag fitted with star tip. Pipe cream decoratively around edge of cake. Arrange toffee pieces in whipped cream border. Refrigerate until serving.

Cut cake into wedges. Serve, passing remaining caramel sauce separately.