In a large mixing bowl, blend softened butter with a hand mixer for about 10 seconds.
Add in sugar and mix until well blended. Beat eggs into the mixture until all incorporated.
Add in vanilla and mix again.
In a separate bowl add flour, cocoa, baking powder, and salt. Whisk together until combined.
Add the dry ingredients to the wet mixture and mix with a spoon until combined.
Fold in chocolate chips and chopped walnuts.
Lightly spray a 7 inch pan with non stick cooking spray. (We used a 7 inch springform pan.)
Add batter to the pan and spread evenly.
Place a 3 inch high trivet in bottom of instant pot and add in 1 1/2 cups water.
Place a folded foil strip about 18 inches long on top of the trivet. This will make it easy to lift out the brownies after they are done cooking. Or you can purchase a silicone lifter.
Place pan into the instant pot and cover with foil. This helps to keep all of the moisture out while they are cooking.
Fold the foil strips loosely over the top of the brownies.
Place lid on instant pot and lock into place. Cook for 55 minutes on high pressure. Then let it do a natural release for 10 minutes. Then do a quick release with the remaining pressure.
When the pressure has all been released, lift the lid carefully and remove pan.
Let cool for about 15 minutes and then remove brownies from the pan. (We removed the sides of the springform pan.)
Serve warm with ice cream.