Place walnuts and almonds in food processor and process until finely ground.
Add the cacao powder and sea salt and pulse to combine.
Transfer to bowl and set aside.
Soak Dates for 1o minutes in warm water if dry. Add the dates to the food processor and process until small bits remain. Remove and set aside.
Add nut and cocoa mixture back into food processor and while processing, drop small handfuls of the date pieces down into the food processor or blender spout.
Process until a dough consistency is achieved, adding more dates if the mixture does not hold together when squeezed in your hand. You may not use all the dates.
Add the brownie mixture to a small parchment lined 8x8 dish and before pressing, add remaining 1/2 cup roughly roughly chopped walnuts and cacao nibs and toss to combine and evenly distribute. Then press down with hands until it is flat and firm. place in freezer or fridge to chill for 4 hours (one hour is usually sufficient if using freezer) If planning to use icing add this before placing in freezer using instructions below.
For the icing:
Place all ingredients in a food processor. If possible, let them sit in there for a few minutes to soften the dates a little bit.
Blend all ingredients in your food processor. . Keep blending for a very long time to get a velvety consistency. If you feel that the blades are just spinning but aren't actually moving all of the icing around, turn the blender off and make an air pocket down the side of the blender with a spatula to expose the blades. Remove the spatula, replace the lid, and start blending slowly again. (Can add more water if needed however best not to if possible)
You'll know it's ready if there are no bits of dates and all you can taste is velvety chocolate goodness. Now it is ready to pour onto the brownies for chilling.
After chilling remove from pan and cut into 8-12 squares and serve. Leftovers can be wrapped individually in waxed paper or parchment and placed in an airtight container in the fridge for up to a week.