Beat egg whites, buttermilk and melted Becel® sticks in medium bowl with wire whisk until blended; set aside. Combine remaining ingredients in large bowl. Stir buttermilk mixture into flour mixture until well combined. Turn into lightly greased 13 x 9-inch (3.5 L) baking pan, smoothing the top.
Bake 15 minutes or until a toothpick inserted in centre comes out clean.
Cool completely on wire rack. Cut into squares to serve. Store refrigerated in an airtight container.