Preheat the oven to 350 degrees and prepare a baking sheet with parchment paper.
In a medium saucepan, cook butter over medium heat while whisking constantly. The butter will begin to foam, and eventually start to turn brown at the bottom of the pan.
Once the butter begins to brown, transfer immediately to a stand mixer fitted with a paddle attachment. Let cool for 5 minutes.
Add sugars and mix until combined.
Add egg, egg yolks, greek yogurt and vanilla extract.
Add dry ingredients and mix until just combined.
Stir in chocolate chips and toffee pieces. (*TIP - Set some chips/toffee pieces aside to put on top of each cookie after they come out of the oven)
Use a medium ice cream scoop to scoop out cookies and place them in the fridge for at least one hour.
Place on baking sheet, 2 inches apart, and bake for 12-15 minutes, or until the edges of the cookies begin to turn golden brown.
Take cookies out transfer to wire rack to cool.