Hersey Cookies and Creame Treat
Basically, you have to either pour the hot one over the cold one, or dip cold in hot.
Freeze the first solid section in the moulds, then set on a wire baking tray &amp; pour over your second layer.  This method will bind to the wire if you're not careful.
Alternatively, dip the cold in the hot &amp; lay on a non-stick surface. This method tends to spread out a bit, so leave plenty of room around each chunk. Alternatively, don't dip to full-depth to allow for some run-off.
DaringGourmet has a recipe showing both methods, though over a different substrate - Marzipan Truffles