Prawn shells and heads contain an extraordinary concentration of flavor that forms the backbone of any serious shellfish broth. The key is a two-stage process: first, sear the shells in hot oil until they turn deep pink-red and develop a caramelized fond on the bottom of the pan — this is where the deep, sweet shellfish intensity lives. Second, after simmering with aromatics and stock, strain the broth through a fine-mesh sieve and press hard on the solids with the back of a ladle, really crushing the shells to extract every drop of liquid. This pressing step is where home cooks most often fall short. A quick pour-through leaves the majority of developed flavor trapped in the strainer. Professional kitchens use a chinois with a pestle for maximum extraction. At home, sustained firm pressure with a ladle against a fine-mesh sieve achieves excellent results — just commit to the effort and don't stop until the solids are dry.