Combine peanut butter and raw cacao butter in a large microwave-safe bowl. Heat on low for 2-3 minutes (or until completely melted), stirring regularly.
Stir in maple syrup and vanilla.
Line a loaf pan with cling film and pour fudge into tin.
Refrigerate 4 hours or overnight (until set).
Serve sprinkled with sea salt and cacao nibs. Store in the refrigerator.
