Preheat the oven to 350 F and line a 8x8 baking pan with parchment paper.

In a small/medium microwave-safe bowl, melt butter until it’s 90% melted, about 1 minute for cold butter or 30 seconds for room temperature butter. Stir until the melted butter melts the leftover (10%) solid butter.

Mix the melted butter and both brown and white granulated sugars in a stand mixer on medium speed for about 2 minutes.

Add egg and egg yolk, vanilla extract, and salt. Mix on low for 30 seconds or until incorporated. Mix in flour and baking soda until just combined. Fold in the Rolos and the Robin Egg Whopper pieces.

Place dough into the prepared baking pan and press down evenly. Place extra Robin Egg pieces on top of the dough.

Bake for 22-26 minutes or until golden on the inside and not jiggly if you carefully shake the pan. Let cool for 15-20 minutes. Enjoy!