I recommend using a silicone muffin tin, but if you don't have one, simply line your cupcake tin with liners.
Add the chocolate chips to a microwave-safe bowl. Microwave in 20-second intervals, stirring between each, until completely smooth. If desired, stir in a teaspoon of coconut oil for a thinner, easier-to-work-with chocolate coating.
Line a cupcake tin with liners (or use a silicone tin for mess-free!). Add some chocolate to the bottom of each one, working it up the sides slightly. Place in the freezer for 10-15 minutes until completely firm.
In the meantime, add the filling ingredients to a bowl and mix until smooth and creamy. Taste and adjust the sweetness if needed.
Add a spoonful of the peanut butter filling to each cup, leaving a little room around the edges. Cover with the remaining melted chocolate and gently smooth the tops.
Place the peanut butter cups in the freezer for at least 1 hour, or until completely firm. Peel away the liners and enjoy straight from the freezer.