Melt chocolate and peanut butter together using the double boiler method, until smooth and combined. Gently stir through the salt.
Pour fudge into a loaf pan lined with baking paper and refrigerate for at least two hours, or overnight.
Remove from the fridge, spinkle flakey sea salt over the top and slice into squares.
Serve straight away or store in the fridge in an airtight container for up to one week.