Preheat the oven to 350℉/176℃. Line 2 baking trays with parchment paper and set aside. Chop the pecans and set aside.
In a pot over medium-high heat, melt the butter. Continuously stir it after melting. It will begin to foam, and after a few minutes you will notice brown specks on the bottom of the pan as you keep stirring. The aroma of nutty, caramel-like brown butter will also arrive. Remove from heat and transfer into a heat-safe glass container to cool as you prep the rest of the ingredients.
3/4 cups + 2 tbsp unsalted butter
In a bowl, add the flour, baking soda, baking powder, cornstarch, cinnamon, and salt. Stir to combine and set aside to use later.
2 cups all-purpose flour, 1/2 tsp salt, 1 tsp cornstarch, 1/2 tsp cinnamon, 1 tsp baking soda, 1/4 tsp baking powder
In a large bowl, add the melted and cooled brown butter, brown sugar, and white sugar. Whisk for 1-2 minutes until well combined.
1/3 cup dark brown sugar, 1/3 cup white sugar, 3/4 cups + 2 tbsp unsalted butter
Add in the egg, egg yolk, and vanilla. Whisk for another 1-2 minutes until smooth.
1 large egg, 1 large egg yolk, 1 tbsp vanilla
Toss in the dry ingredients. With a spatula, gently stir just until a soft cookie dough forms. Do not over-mix!
Add in the chocolate chips, chopped pecans, and toffee bits. Mix in a few times to evenly distribute them into the dough.
1/2 cup semi-sweet chocolate chips, 1/2 cup pecans, 1/2 cup toffee bits
Scoop 6 cookies per tray, spacing them evenly apart from one another. Bake for 14-17 minutes or until they have golden crisp edges and soft, puffy middles. I baked mine for 16 minutes exactly. For gooey-er cookies, bake them for less time. The cookies may look underbaked in the middle, but will continue to bake as they cool.
Allow to cool, transfer to a cooling rack, and enjoy!