Preheat oven to 200 degrees F (95 degrees C). Line a 9x13-inch baking dish with parchment paper.
Blend almond milk, 1 cup maple syrup, vanilla extract, and 1 1/2 teaspoon salt in a blender. Mix in 3 cups cocoa powder. Pour batter into a large bowl; fold in ground almonds and ground cashews. Pour batter into prepared baking dish; spread evenly to 1/2-inch thickness.
Bake in preheated oven until top is dry and edges have started to pull away from the sides of the pan, about 1 hour. Remove from oven and cool completely, about 30 minutes.
Blend 3 cups cocoa powder, coconut oil, 3 tablespoons maple syrup, cinnamon, and pinch of sea salt together in blender; spread ganache mixture over brownies.
Refrigerate brownies to set, about 30 minutes; cut into squares.