Line a muffin tin with cupcake cases. Place the dark chocolate chunks and coconut oil into a microwave safe bowl and microwave for 30 second intervals until melted, stirring each time. Stir in the vanilla extract.
Pour half of the chocolate mixture into the cupcake cases and place in the freezer for around 5 minutes. Meanwhile, place the peanut butter, salt and coconut oil into a bowl/mug and microwave for around 15-20 seconds and stir well.
Take the cupcake cases out of the freezer and pour the peanut butter mixture evenly into the cupcake cases. Once again, put them in the freezer for 5 more minutes to set.
Pour the remaining chocolate mixture on top of the peanut layer and place in the fridge for 10-15 minutes.