In a heat proof bowl add chopped chocolate and pour hot boiling water over it. Using a spatula give everything a good mix until the chocolate has dissolved completely.
Place the bowl with the chocolate mixture over an ice bath, and start whisking using an electric whisk for about 3-5 minutes until a light and fluffy chocolate mousse like texture is achieved. Transfer the mousse to the serving glass of your choice.
For the crumble, preheat your oven at 160C.
In a bowl add walnuts, brown sugar, flour and cold cubed butter. Using your hands gently rub the butter into all the ingredients until the mixture resembles sand.
Transfer the crumble to a baking tray lined with parchment paper and gently pat the crumble down to flatten it.
Bake for about 8-10 minutes or until the crumble is golden brown.
Top the mousse with the walnut crumble and enjoy!
Recipe by Bake with Shivesh at https://bakewithshivesh.com/easy-chocolate-mousse-2-ingredient-mousse-recipe/