Combine heavy cream and caramels in a small microwave-safe bowl; microwave at HIGH 2 to 3 minutes or until caramels are melted, stirring after every minute. Stir in nuts, pretzels, and vanilla. Spoon mixture into 45 (1 1/2") foil petits four cups lightly greased with cooking spray, filling each two-thirds full; cool completely.
Place chocolate morsels in a small microwave-safe bowl, and microwave at HIGH 1 minute or until melted; stir until smooth. Spoon chocolate evenly over caramel in cups; cool slightly. Sprinkle with fleur de sel, and let candy cups set completely. Store candy cups in an airtight container in a cool, dry place.