Combine sugar and salt in a heavy skillet. Heat over high heat until sugar lumps. Lower heat and continue cooking , stirring until sugar is completely melted. It will be a rich caramel color. stir in nuts and butter. Pour immediately into a greased jelly roll pan.
Melt butter in a saucepan. Blend in flour and cook for one minute until mixture bubbles Remove from heat and gradually whisk in milk. Cook until thickened while stirring constantly. Remove from heat and blend in cheddar cheese until melted. Separate eggs. Take yolks and add to cheddar cheese mixture. Mix well.
Beat egg whites until stiff. Fold egg whites into sauce. Put the mixture into an ungreased casserole. Bake at 300 degrees for 1 1/4 hours.