In a food processor, blend chocolate layer ingredients until smooth.
Transfer chocolate mixture to a small glass container lined with parchment paper. Using a rubber spatula or a spoon to spread the mixture out evenly and push down firmly into the container.
In a small bowl, mix together peanut butter layer ingredients until combined.
Use a spoon to transfer the peanut butter layer on top of the chocolate fudge. Spread it out evenly. Sprinkle flaky salt on top, if using.
Cover freezer fudge and place in the freezer for at least 1 hour. When ready to eat, cut the fudge into small squares and eat right away. Store in the freezer so the fudge doesn't melt.