Place crackers in a single layer in a foil-lined 15x10x1 baking pan.
In a saucepan, bring butter and sugar to a boil. Reduce heat; 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. Chill for 15-20 minutes or until set. Break into pieces. Store in refrigerator.