In a saucepan, bring butter and sugar to a boil.
Reduce heat and simmer uncovered for 5-6 minutes or until mixture is thickened and sugar is completely dissolved.
Spread over crackers.
Bake at 350° for 7-8 minutes or until bubbly.
Sprinkle with chocolate chips. Bake 3-5 minutes longer or until chips begin to melt.
Spread chocolate evenly over top.
Melt white chocolate and shortening, drizzle over toffee.
Sprinkle with crushed saltine crackers, if desired.
Chill for 15-20 minutes.