PREHEAT oven to 350º F. Grease 13 x 9-inch baking pan.
COMBINE flour and brown sugar in large bowl. Cut in butter with pastry blender or 2 knives until mixture resembles coarse crumbs. Press onto bottom of prepared baking pan.
BAKE for 12 to 15 minutes or until light golden brown.
COMBINE sweetened condensed milk, eggs, butter and vanilla extract in same bowl. Stir in pecans. Sprinkle shortbread base with 1 cup morsels. Pour pecan mixture over morsels. Sprinkle remaining morsels over top of pecan mixture.
BAKE for 20 to 25 minutes until lightly browned around edges and center is set. Cool completely in pan on wire rack. Cut into bars.