Heat oven to 350°F. Spray bottom of 13x9-inch baking pan with non-stick cooking spray. In large bowl, combine flour, 1/2 cup brown sugar and butter. Spread on bottom of prepared pan. Bake for 20 minutes.

In medium bowl, beat together egg, sweetened condensed milk, vanilla and remaining brown sugar. Stir in pecans. Pour on top of baked cookie layer. Bake 25 minutes. Cool. Cut into bars. Store leftovers covered at room temperature.