Place the chocolate melts in a heatproof bowl over a saucepan of simmering water (don't let the bowl touch the water). Stir until the chocolate melts and is smooth.
Place the hundreds and thousands in a shallow bowl. Dip the tops of half the biscuits in the melted chocolate, then into the hundreds and thousands to coat. Place on a baking tray. Place in the freezer for 5 minutes to set.
Place the remaining biscuits, base-side up, on a clean work surface. Divide the ice-cream among the biscuit bases.
Top with the chocolate-coated biscuits. Serve immediately.