In a large stock pot over medium heat, melt the butter.
Add marshmallows; cook and stir until marshmallows are mostly melted.
Stir in vanilla, molasses, ginger, and clove.
Remove from heat, and quickly stir in gingersnap cookie crumbs and Rice Krispies cereal.
Press into the bottom of a buttered 13x9-inch pan.
In a small microwave-safe bowl, combine the white chocolate chips and shortening.
Heat at 20-second intervals until melted and smooth. Do not increase heat time intervals - the chocolate MUST melt slowly or it will scorch and turn clumpy. Short intervals, with stirring in between, until melted and smooth.
Spread melted chocolate evenly over bars.
Allow to set, about 15-20 minutes. Cut into bars.