Preheat the oven 350℉. Line an 8-inch metal baking pan with foil. Spray the foil and any exposed sides of the pan with cooking spray.
Line a baking sheet with foil and lay the nuts out on the foil Bake in the oven for about 5-7 minutes to toast the nuts. Remove from oven and toss all of them together in a small bowl. Set aside.
Mix cocoa powder, flour, salt, baking soda and cornstarch in a small bowl. Set aside.
Melt the butter in a sauce pan over medium-low heat. Add sugar and stir into the melted butter. Remove from stove. Add eggs, one at a time, blending well after each with a whisk or wooden spoon.
Add oil and vanilla and mix well. Stir in the flour mixture and mix well. Stir in chocolate chips (and chopped nuts if you’re adding them to the batter instead of on top.)
Spread the batter into the prepared pan and cover with the toasted nuts.
Bake in 350℉ oven for 25-30 minutes. Even if they are still soft, remove from oven as they will continue to cook from the heat of the pan. Cool completely before cutting into 2-inch squares.
Store them in an airtight container in the refrigerator.