1. For the nam jim sauce, place garlic in a mortar and pound lightly so you can remove the garlic skins. Add coriander root and pound to a rough paste. Stir in fish sauce, sugar and lime juice. Stir through chillies, adding more or less to taste.
2. Grill whole prawns and squid on a hot BBQ grill plate until just cooked through (about 3-4 minutes per side). Slice squid into bit sized pieces. Serve squid and whole prawns with nam jim dipping sauce.