Prepare a 9x13 pan by greasing it and/or lining it with parchment paper. Melt butter and mini marshmallows over medium low heat until smooth, stirring all of the time to prevent scorching.
Stir in Rice Krispies, press into a 9×13 pan (or slightly smaller if you prefer a thicker Rice Krispie).
Melt caramels, vanilla and 1/4 cups heavy cream over a double boiler, until smooth. It will take about 10 minutes, stir as needed. Pour over Rice Krispie Treats. Place the pan in the fridge for about 5 minutes.
Melt the chocolate chips and 1/4 cups of heavy cream in the microwave for about 1 minute. Spread over caramel.
Sprinkle chopped pecans, and additional chocolate chips over the chocolate layer and let it set in the fridge. Drizzle the remaining caramel and chocolate. Cut into squares and serve.