Melt the chocolate base: Break the 200g sugar-free dark chocolate into small, even pieces and place in a heatproof bowl set over a pan of simmering water. Stir gently with a spatula until the chocolate is completely smooth and glossy — you’ll see it turn from solid shards into a silky, dark puddle with a rich, bitter cocoa aroma. Remove from the heat and stir in half the melted coconut oil until fully incorporated.

Prepare the muffin liners: Line a 12-hole muffin tin with paper cases. Using a small spoon, drop about one teaspoon of the melted chocolate into the bottom of each liner. Tilt the tin gently so the chocolate spreads evenly across the base. You should see a thin, dark layer covering the entire bottom of each case. Place the tin in the freezer for 10 minutes, or until the chocolate is firm and matte to the touch.

Make the peanut butter filling: In a separate bowl, combine the 100g peanut butter, the remaining melted coconut oil, the powdered erythritol or stevia, and the vanilla extract. Stir vigorously — the mixture will start stiff but quickly become a thick, spreadable paste with a nutty, sweet scent. Taste and adjust sweetness if needed; the filling should be just a touch sweeter than you want the final cup to be, as the chocolate will balance it.

Fill the cups: Remove the tin from the freezer. Spoon a heaped teaspoon of the peanut butter mixture into each chocolate-lined cup. Press it down gently with the back of the spoon so it flattens into an even layer, leaving about 3mm of space at the top for the final chocolate seal. The filling should look pale and creamy against the dark chocolate.

Add the top chocolate layer: Reheat the remaining melted chocolate briefly if it has thickened (10 seconds in the microwave or a quick stir over the simmering water). Spoon one teaspoon of chocolate over each peanut butter layer, spreading it gently to the edges of the liner. Tap the tin firmly on the counter a couple of times — you’ll see the chocolate settle and any air bubbles rise to the surface. Sprinkle a tiny pinch of sea salt over each cup.

Set the cups: Return the tin to the freezer for a full 20 minutes, or until the tops are completely firm and release easily from the paper liners. When ready, the cups should pop out cleanly with a slight snap when you bend the paper away. Store in an airtight container in the fridge for up to two weeks, or freeze for up to three months.