Preheat the oven to 350°F. Prep an 8x8 pan by lining with parchment paper and spraying with cooking spray. Set aside.
In a saucepan over medium heat, melt your butter. Once melted, the butter will begin to foam. Continue stirring (don’t stop!) for 5-8 minutes. After this time, you’ll notice two things: browned specks at the bottom of your pan, and a nutty aroma that will fill the air. Remove from heat, transfer to a glass container and cool for 20 minutes before using.
In a medium sized bowl, whisk the browned butter and sugar.
3/4 cups butter, 1/2 cup brown sugar
Add in egg, egg yolk, and vanilla and continue whisking.
1 egg, 1 egg yolk, 1 tbsp vanilla
Switch to a spatula and fold in the flour, cornstarch, baking powder, and salt. Once nearly combined add in the dark chocolate, and toffee pieces. Mix until there are no more dry streaks.
2 cups all-purpose flour, 1 tbsp cornstarch, 1 tsp baking powder, 1/2 tsp salt
Transfer into prepared pan and spread evenly. Add extra dark chocolate and toffee pieces if desired.
1/2 cup toffee bits, 1/2 cup dark chocolate chips
Bake for 25-27 minutes or until a toothpick inserted comes out clean. The edges will have a slight golden brown look. Allow to cool in the pan for at least 20 minutes before slicing. Add a dash of sea salt on top for extra flavour! Enjoy!