Step 1

Preheat oven to 350 degrees. Line a 9x13 baking dish with foil and lightly spray with baking spray such as Pam, set aside.

Step 2

In the bowl of a stand mixer, beat melted butter, sugars and vanilla until light and fluffy, about 2 minutes. Add eggs and yolk, one at a time, mixing until incorporated.

Step 3

In a medium size mixing bowl whisk together flour, cocoa powder, baking powder, cornstarch, and salt. With mixing speed on low, alternate adding dry ingredients and milk. Mix just until combined.

Step 4

Remove bowl from stand and pour batter into prepared pan. The batter will be thick, so using a rubber spatula, spread into an even layer. Place in oven and bake for 18-22 minutes (I live in high altitude so my bars tend to bake quicker). The brownies will be done, so do not over-bake or you will have dry brownies! Remove from oven and allow to cool in the pan.

Step 5

Meanwhile to prepare the ganache, in a 2 c. glass measuring cup, combine chocolate chips and heavy cream. Microwave on half powder (mine is usually power 10, so I did for one minute, stir, then repeat. Stir chocolate until all of the chips are melted and it becomes smooth. Beat for 1 minute and then pour over the top of the brownies. Spread evenly and sprinkle chopped walnuts. Cover and place in the refrigerator to allow the topping to set for at least 30 minutes.