Heat over to 350. In a medium bowl blend thoroughly butter, brown sugar and flour with a fork until mixture resembles coarse crumbs. Put 1 cup of the mixture aside for topping. Press remaining mixture into an 8x8x2 inch baking dish; bake for 15 minutes. In another bowl combine sugar and cream cheese, mixing until smooth. Thoroughly beat in egg, milk, lemon juice and vanilla. Spread over the baked crust and sprinkle with remaining brown sugar mixture. Bake for 25 minutes. Let cool, then chill for at least 1 hour. Cut into 16 squares; serve.