While dates are soaking, place 1 1/2cups walnuts in a food processor until crumbly. Then add in the cocoa powder, peanut butter, and salt. Set mixture aside in a bowl. Then once dates have soaked for about 10 minutes, place them in food processor and blend until it makes somewhat of a paste. Add in vanilla and water, process again for a few second. Take the dates out and place in bowl.
Then, put the cocoa powder mixture back in, and gradually add in dates on low speed. It will look crumbly but don't add in any more liquid!
Line an 8x8 dish with parchment paper and dump mixture into dish. Press mixture down until roughly distributed. Then add cacao nibs and remaining walnuts on top. Press evenly all the way around. Place in freezer while you make the frosting.
In a bowl, mix together all of the ingredients for the frosting. It should be a smooth consistency. Spread on top of brownies and then place in fridge for 1 1/2 -2 hours. Then enjoy! These keep well in the freezer too.