In a large stockpot, bring the water, beer, sea salt, brown sugar, and 2 sprigs of crown dill to a boil. Boil the crayfish in batches of 3-4 at a time. Cook for 2-4 minutes or until bright red. Using a slotted spoon, remove the crayfish and allow them to cool. Remove the dill, and cool the boiling mixture. In a clean bowl, add the cooled crayfish and liquid mixture, plus the remaining dill. Cover and refrigerate for at least 6 hours, or ideally overnight.
Serve the crayfish in a large bowl with a ladle or two of the liquid mixture. I also suggest serving the crayfish with buttered and toasted white bread, fresh lemon wedges, and aioli on the side.