Cream together butter and brown sugar until light and fluffy. Add flour and walnuts; mix well. RESERVE 3/4 cup mixture for topping. Press remaining mixture into greased 8 inch square baking pan. Bake in 350°F oven 12 to 15 minutes.
Beat together sugar and cream cheese until smooth. Beat in egg, milk, lemon juice and vanilla; mix well. Spread over baked crust. Sprinkle with reserved crumbs.
Bake in 350°F oven 25 minutes or until done. Cool in pan on rack. Cut in 2 inch squares. Makes 16 squares.