Combine Nutella and powdered sugar in a small bowl.
Line a mini muffin pan with paper liners.
In a double boiler, melt the chocolate chips. (To do this, put the chocolate chips in a heatproof bowl, and place the bowl in a pot of boiling water. Ideally, the bowl will not come into contact with water. It's best to use a bowl large enough to prevent the water from getting into the bowl.)
Spoon a small amount of melted chocolate into the bottom of each paper liner.
Scoop a clump of Nutella into each cup on top of the melted chocolate.
Spoon melted chocolate over top of the Nutella, filling the cup to the top.
Sprinkle a few flakes of sea salt on to the top of each cup.
Place in the freezer for approximately 30 minutes, or until chocolate has hardened.
Remove from freezer, and allow to sit for a few minutes before taking a bite! These are best at room temperature if you're patient enough to wait - just don't break your teeth on a frozen one!