Make the dark chocolate by melting the cacao butter in a double-boiler or bain marie over medium heat. Once it's melted, remove from the heat and whisk in the cacao powder and maple syrup until smooth.

Line a muffin tin with 5 cupcake liners. Pour 1 tablespoon of the dark chocolate into the bottom of each muffin liner and carefully rotate the pan around and around to coat the sides of the muffin liners with the chocolate. You want the chocolate to go up about ½ and inch on all sides of each liner. Place pan in freezer for 10 minutes to set.

Meanwhile, make the peanut butter caramel by combining the peanut butter, maple syrup, coconut oil, vanilla extract, and sea salt in a small saucepan. Whisk together over medium-low heat until completely smooth. Chill in freezer for 10 minutes to thicken.

Drop 1 heaping tablespoon of the peanut butter caramel into the center of the chocolate cups (use up all of the caramel) and carefully spread it out to the sides of each cup. Then, pour heaping tablespoons of the chocolate over the caramel layer, using up all of the chocolate. If needed, drop the pan on a hard surface a few times to smooth out the surface of the chocolate. If desired, sprinkle with large-flake sea salt. Return to freezer for 10 minutes to set. Store in refrigerator.