First, check both the white and brown meat for any bits of shell that might have snug in. This is best done with your bare hands, the pieces can be quite small. For the crab salad, combine the lime juice, brown sugar and fish sauce in a bowl, stir until the sugar has dissolved. If your sugar is quite hard, you can heat the mixture a little to make the dissolving easier. Finely chop the coriander, mint and kaffir lime leaves, deseed and de-vein the chilli and chop finely as well. Combine all ingredients in a bowl and leave to infuse for at least 3 hours in the fridge. You can prepare this a day in advance, if you wish. For the brown meat mayo, chop the brown crab meat roughly, then mash with a fork. Combine with the mayo/aioli and seaon with salt, pepper and a dash of tabasco. Shred the lettuce leaves thinly, then cop roughly. To assemble, place about half a tsp of the brown mayo on the bottom of each croustade, fill the shells up with shredded lettuce about half way, then top with about 1 tsp of the crab salad. Serve within 30 minutes to an hour so the bases don't get soggy.