Combine the dates, walnuts, 6 tbsp cocoa, 1 1/2 tsp vanilla, water, and salt in a food processor. Blend until completely smooth, scraping down as needed. It may be a little dry but don't add any water.
Lightly grease an 8-inch square baking pan, or line the pan baking paper.
Transfer dough to pan and press very firmly until dough is evenly distributed in the pan.
In a medium mixing bowl, combine remaining cocoa and vanilla extract with the maple syrup and oil. Stir until mixture forms a paste (this is the frosting). Spread evenly over dough in the baking pan.
Refrigerate brownies for at least 2 hours, to set. Leftovers can stay covered at room temperature for a day, or up to 2 weeks in the fridge.
* you can use Cocoa powder instead of Cacao