In a small bowl, cream butter and brown sugar until light and fluffy. Gradually add flour to creamed mixture and mix well. Stir in pecans.
Set aside 1 cup for topping. Press the remaining mixture into a greased 8-in. square baking pan. Bake at 350° for 10-12 minutes or until set. Cool on a wire rack.
In another small bowl, beat cream cheese and sugar until smooth. Add egg, beating just until combined. Beat in the cream, lemon juice, peel and vanilla. Spread over crust. Sprinkle with reserved topping.
Bake at 350° for 20-22 minutes or until center is almost set. Cool on a wire rack for 1 hour. Refrigerate overnight. Cut into diamonds. Refrigerate leftovers.