Step 1

Preheat the oven to 350°F. Line a 9×13 pan with parchment paper and coat with nonstick spray. Set aside.

Step 2

In the bowl of your stand mixer fitted with the paddle attachment mix the butter and the light and dark brown sugars together for 2 minutes on medium speed. Add in the eggs, vanilla, salt and baking powder and mix for an additional minute on medium, scraping the sides of the bowl as necessary.

Step 3

Turn the mixer to low and add in the flour, mixing until just combined.

Step 4

Finally add in both kinds of chocolate and stir to incorporate.

Step 5

Spread the dough into the prepared pan and bake for 30 minutes or until the edges are set and lightly golden and the center appears slightly under-baked.

Step 6

Remove the pan from the oven and allow the bars to cool completely before cutting.

Step 7

Alternately you can chill the bars before cutting.