Line a 12-cup muffin tin with paper liners and place a baking sheet nearby.
Melt about two-thirds of the chocolate in a heatproof bowl over simmering water or in short microwave bursts, stirring until smooth.
Optional: stir in 1–2 tablespoons coconut oil for a glossier finish; remove from heat.
Spoon about 1 teaspoon of melted chocolate into each liner and tilt to coat the bottom and part of the sides; reserve chocolate for sealing.
Chill the tray for 5–10 minutes to set the first chocolate layer.
In a bowl, beat together peanut butter, powdered sugar, softened butter, vanilla, and salt until smooth and thick.
Divide the peanut butter mixture into 12 even portions, flatten each slightly, and place one onto each chilled chocolate base, leaving a small gap at the edges.
Reheat remaining chocolate briefly if needed and spoon over each filled cup to fully seal and smooth the tops.
Optionally sprinkle a tiny pinch of flaky sea salt on each top.
Refrigerate the cups for 30–60 minutes until fully set, then remove liners and serve or store.