Melt the chocolate. I find the easiest way to do this without burning it is to fill a medium-large pot with water and bring to a boil.
Place a large stainless steel bowl on top of the pot and place 2 cups of the chocolate chips in. Stir frequently as they melt.
Once melted, "paint" the inside of the silicone baking cups with the melted chocolate, using a pastry brush so there is a thin layer of chocolate. Don't worry - it's pretty forgiving! Doesn't need to be perfect. Just cover the inside of the cup.
Paint all 24 cups. Place the tray of painted silicone cups into the freezer for approximately 30 minutes or until completely frozen and set.
As the cups freeze, add the other 1 cup of chocolate chips to your bowl to melt them. Again, stir as they melt. Make sure you don't boil off all the water in your pot - check periodically.
Once the first layer is set and hard, take the tray out of the freezer and fill each cup ¾ of the way with the peanut butter.
Then top each cup with more melted chocolate. It's okay if it spills over a bit. Sprinkle a few grains of rock salt on each one.