Add the pitted dates to a large bowl and cover with boiling water. Let sit for 5-10 minutes to soften.
Place the walnuts, almonds, cacao powder and salt into the bowl of a food processor and process until the nuts are chopped and everything is blended. Drain and add the dates and process until the mixture holds together when you squeeze it between your fingers. Press the mixture into a 9x9 pan lined with parchment. Use the back of a spoon to smooth the top into the corners and to make everything level.
Heat the almond milk in the microwave for 30-45 seconds until scalded. You could also heat the milk in a small saucepan if preferred. Add the chocolate chips and let sit for 5 minutes or until melted. Gently stir the mixture until thick and fudgy and pour the mixture on top of the prepared pan and smooth with a spatula. Sprinkle with the 1/4 cup chopped walnuts. Refrigerate or freeze the brownies for an hour so they will be easy to slice. When ready to serve slice into 16 pieces and store in an airtight container in the fridge or freezer for up to a week.