For the brownies
In a food processor add almonds and walnuts and process until they are finely ground. Transfer to bowl and set aside.
Add Medjool dates and warm water to the food processor and blend until small bits remain - if too dry add a little more warm water. Add almond and walnut mixture and process with remaining ingredients. Stopping to scrape ingredients down. Remove blade and mix the remaining 1/2 cup roughly chopped walnuts by hand.
Transfer mixture to a parchment lined 8x8 dish and gently press to flatten. Rose places a piece of plastic wrap like Saran Wrap over mixture before pressing to flatten. Chill for 15 minutes before frosting.
For the frosting
Add pitted Medjool dates and boiling water to the food processor and blend until the dates form a paste.
Add remaining ingredients and blend until smooth.
Spread over chilled brownies.
*While Medjool dates are high in natural sugars, they are low on the glycemic index thanks to a balanced amount of soluble fiber. The complex carbohydrates found in Medjool dates are digested at a slower rate, making them a source of dietary fiber and releasing energy to the body over a longer period of time.