Sift flour and sugars together in large bowl.
Cut butter into small pieces add add to dry ingredients.
Combine with mixer or fingers until butter incorporated - will be sandy texture, but should clump together when pressed.
Grease large baking pan w/ butter and flour.
Press mixture firmly into pan
Bake at 350 for 30 minutes - top should be very light brown.
Cut into desired pieces with very sharp knife immediately, then allow to cool.