Prep the pan. Line a mini muffin tin with paper liners or use silicone molds.
This keeps the cups from sticking and makes clean-up easy.
Make the chocolate base. In a microwave-safe bowl, combine 1/2 cup sugar-free chocolate chips with 1 tablespoon coconut oil. Microwave in 20–30 second bursts, stirring between each, until smooth. Stir in 1/2 to 1 tablespoon powdered sweetener if you prefer sweeter chocolate.
Layer the chocolate. Spoon about 1 teaspoon of melted chocolate into each cup.
Tilt the pan slightly so the chocolate spreads evenly across the bottom. Place the tray in the freezer for 5–7 minutes to set.
Mix the peanut butter layer. In a small saucepan over low heat, gently melt 1/2 cup peanut butter with 2 tablespoons coconut oil and 2 tablespoons unsalted butter. Stir until smooth.
Remove from heat and whisk in 1–2 tablespoons powdered sweetener, vanilla, and a pinch of sea salt. Taste and adjust sweetness.
Add the peanut layer. Remove the chilled chocolate bases. Spoon 1 to 1 1/2 teaspoons of the peanut mixture into each cup, leaving a little room on top.
If you like a thicker center, go up to 2 teaspoons. Freeze for 10 minutes.
Top with chocolate. Rewarm the remaining chocolate if it has thickened. Spoon another thin layer over each cup to fully cover the peanut filling.
Gently tap the pan to level the tops.
Set and finish. Freeze for 15–20 minutes until firm. Sprinkle a tiny pinch of flaky sea salt on top if you like a sweet-salty finish.
Serve. Pop the cups out of the molds. Let sit at room temperature for 2–3 minutes before eating for the best texture.