Line a 12-cup mini muffin tin with paper liners. Melt the sugar-free dark chocolate and coconut oil together in a microwave-safe bowl in 20-second intervals, stirring between each, until completely smooth.
Spoon about 1 teaspoon of melted chocolate into each liner. Use the back of the spoon or a small brush to push the chocolate slightly up the sides, creating a small cup shape. Place the tin in the freezer for 10 minutes to set.
While the chocolate sets, stir together the tahini, powdered erythritol, melted coconut oil, vanilla extract, and a pinch of salt until smooth and creamy.
Remove the tin from the freezer and drop about 1 teaspoon of the tahini filling into each chocolate cup. Gently press it down to flatten, leaving a small border of chocolate visible around the edges.
Spoon the remaining melted chocolate over the tahini layer in each cup, covering the filling completely. Tap the tin gently on the counter to level the tops and remove air bubbles.
Sprinkle a few flakes of sea salt on top of each cup. Refrigerate for at least 30 minutes until the chocolate is completely firm. Peel off the liners and enjoy chilled.
