In a medium bowl, mix flour and brown sugar. Cut in butter until mixture resembles fine crumbs. Set aside 1/2 cup for topping; press remaining crumbs into an ungreased 8-in. square baking pan. Bake at 350° for 15 minutes.
Meanwhile, in a bowl, beat cream cheese on medium speed for 30 seconds. Add sugar; beat until fluffy. Add egg, milk, lemon zest, juice and vanilla; mix well. Spread over baked crust. Combine nuts with reserved crumbs; sprinkle over cream cheese mixture. Bake 20-25 minutes longer or until done. Cool on a wire rack.