Line Your Molds
Place mini cupcake liners (paper or foil) into a mini muffin tin.

Make the Chocolate Shells
Melt about two-thirds of the chocolate in a microwave or over a double boiler.
Spoon a small amount into each liner, then use the back of a spoon or a small brush to spread up the sides to form a cup. Chill in the refrigerator until the chocolate sets.

Prepare the Caramel Filling
In a heavy saucepan over medium heat, melt the sugar without stirring too much, until it becomes a golden amber. Carefully whisk in the heavy cream, then the butter, and bring the mixture to a gentle simmer until smooth and slightly thickened. Remove from heat and stir in the vanilla if using. Let the caramel cool slightly until it thickens but still pourable.

Fill the Cups
Spoon a small amount of the cooled-but-still-pourable caramel into each chocolate shell, leaving a little space at the top for the lid.

Seal with Chocolate
Melt the remaining chocolate (if necessary), then spoon or pipe a layer on top of the caramel in each cup to seal it. Gently tap the tin to smooth the tops.

Decorate & Set
Immediately sprinkle the top of each cup with your chosen decorations: holiday sprinkles, a pinch of sea salt, or even tiny nut pieces. Chill in the refrigerator until the chocolate is fully set.

Serve
Once firm, remove the chocolate cups from the liners and serve. Keep them chilled until just before serving for best texture.