Line a muffin tin with paper liners.
In a mixing bowl, combine peanut butter, powdered sugar, and vanilla extract until smooth.
In a saucepan, melt the chocolate chips and butter over low heat, stirring constantly.
Spoon a layer of melted chocolate into each muffin liner, filling them about 1/3 full.
Place the muffin tin in the refrigerator for 10 minutes to set the chocolate.
Add a spoonful of the peanut butter mixture on top of the chocolate layer.
Pour more melted chocolate over the peanut butter layer until it’s covered.
Sprinkle a pinch of sea salt on top, if desired.
Return the tin to the refrigerator for at least 30 minutes to fully set.
Enjoy your homemade peanut butter cups!