Preheat oven to 350*. Line a 13x9x2 inch baking pan with foil. Lightly grease foil; set pan aside.
For crust: Stir together crushed graham crackers and 1/4 c sugar. Mix in 1/3 c butter. Press evenly onto bottom of prepared pan; set aside.
For filling: Beat cream cheese and brown sugar until mixed. Add eggs, one at a time, beating on low speed after each addition just until combined. Stir in concentrate, peel, vanilla and salt. Reserve 1 cup filling in bowl; set aside.
In small saucepan, melt chocolate and 2 tablespoons butter over very low heat; stir often. Cool. Stir into reserved filling. Carefully spread over crust. Bake 15 minutes. Remove from oven.
Carefully pour remaining filling over baked chocolate layer; spread evenly. Bake 40 to 45 minutes or until just set in center. Remove from oven; cool 30 minutes. Combine sour cream and 1/3 cup sugar. Cover; let stand at room temperature while bars cool.
Spread sour cream mixture on bars. Cool. Refrigerate several hours or overnight before cutting. If desired, sprinkle with ground cinnamon before cutting into bars. Store, covered, in refrigerator.