Line an 8x8 inch baking pan with parchment paper, leaving overhang on two sides for easy removal.
In a mixing bowl, stir together the peanut butter, melted coconut oil, powdered erythritol, vanilla extract, and pinch of sea salt until completely smooth and well combined. Pour the mixture into the prepared pan and spread evenly with a spatula. Place in the freezer for 15 minutes to firm up.
While the peanut butter layer sets, melt the sugar-free dark chocolate and coconut oil together in a microwave-safe bowl in 30-second intervals, stirring between each, until perfectly smooth.
Remove the pan from the freezer. Pour the melted chocolate evenly over the peanut butter layer and tilt the pan to spread it into an even coating. Sprinkle flaky sea salt generously over the top.
Return the pan to the freezer for 20 to 25 minutes until the chocolate is fully set. Use the parchment overhang to lift the slab out, then cut into 16 bars. Store in the refrigerator in an airtight container.
