Preheat oven to 350 degrees. Prepare a 9x9" baking pan with non stick spray or butter and flour
In a medium bowl or the bowl of a stand mixer, add oil sugar and vanilla and mix until combined. Add eggs and continue to beat for about one minute. In a separate bowl, combine the flour, cocoa, baking powder and salt and gradually add to the wet ingredients while beating on medium until well combined. Add walnuts and spread the batter into the prepared pan.
Bake for 30 to 35 minutes or until an inserted toothpick comes out clean and the brownie edges begin to pull away from the sides of the pan. Allow to cool before serving.
Preheat oven to 350 degrees. Place chopped nuts on a baking sheet and toast for about 5-7 minutes or until they are fragrant. Remove from oven and allow to cool.
To prevent burning, melt chocolate in a bowl over boiling water in a sauce pan. Once melted, remove from heat and stir in condensed milk, vanilla, baking soda and salt until smooth. Stir in Walnuts or pistachios. Immediately spread in a 8"x8" parchment lined pan and refrigerate until set (about 2 hours) Cut into squares and serve.