Line a 15x10x1-inch baking sheet with parchment paper. Set aside.

In a large saucepan, melt butter over medium heat. Once melted, add in all but 1.5 cups of the marshmallows. Reduce heat to low and continue stirring until completely melted.

Remove from heat and stir in the vanilla extract. Add the cereal and reserved marshmallows. Fold gently until combined.

Pour into the prepared baking dish. Press GENTLY with your fingertips until spread out.

In a microwave-safe bowl, combine caramel bits with heavy cream. Heat for 1.5 minutes, stirring every 30 seconds until smooth. Spread over the Rice Krispie treats. Allow to set about two hours.

Cut into large squares. If desired, drizzle with melted chocolate and add candy bits. Allow to set about 15 minutes before serving. Store covered at room temperature.