Prepare an 8x8" baking pan by lining it with baking parchment or a silicone mat.

To toast the walnuts, heat a small skillet over a medium heat. Add the chopped walnuts to the dry pan, and cook for about five minutes, stirring frequently. Set aside.

Add unsweetened almond milk, heavy cream, coconut oil, and sweetener to a saucepan and heat over a low heat. Stir until the sweetener has dissolved and the mixture is fully combined.

Break unsweetened chocolate into squares and add them to the milk mixture. Continue to cook, stirring regularly, until the chocolate has melted and has been incorporated into the liquid. Add in the walnuts, then pour the mixture into the prepared baking pan.

Leave to cool, then transfer the pan to the fridge. When the fudge has set, turn it out onto a chopping board and cut into 16 squares.

Store in the fridge.