For the pepper sauce, put the lime in a small saucepan and cover with cold salted water. Bring to the boil and cook the lime until soft and tender, about 15-20 minutes. Set aside to cool.
In the meantime, place all the other ingredients, except the salt and pepper, into a blender and pulse until smooth.
Finely chop the lime (keeping the peel on), discarding any seeds, and stir into the other ingredients. Transfer to a sterilised bottle or jam jar, cover with the lid and leave to ‘develop’ for a minimum of 2 days, then season to taste with freshly ground pepper and lots of salt. Give the bottle a good shake to distribute the seasoning. Store in the fridge for up to 6 months (don’t worry about any discolouration over time).
For the fried bakes, mix the flour and salt in a large bowl then use your fingertips to rub in the butter until it resembles fine breadcrumbs. Gradually add 150-200ml/5-7fl oz water (you may not need to use it all), mixing with a spoon, until a dough forms.
Tip the dough out onto a lightly floured work surface, rub your hands with rapeseed oil and knead, for about a minute or so, until the dough is smooth. Shape into a ball and pour a drop of oil on to your palm and coat the dough. Cover the dough in cling film and leave it to prove for 30 minutes in a warm place.
For the buljol butties, rinse the salt cod, place in a large saucepan, cover with fresh water and bring to the boil. Once the water begins to boil, remove the pan from the heat, pour away the water, add fresh cold water and bring to the boil again. As soon as the water starts to boil, reduce the heat and simmer for about 5-10 minutes, until the salt cod is cooked through. Drain the salt cod and set aside to cool.
When the salt cod is cool enough to handle, finely flake the fish into a bowl, taking care to discard any pin bones and skin. Gently but thoroughly mix in the remaining ingredients and season to taste with salt and pepper.
For the fried bakes, heat the groundnut oil to 180C in a deep-fat fryer. Alternatively, fill a large, deep heavy-based saucepan two-thirds full and heat until a small piece of bread turns golden-brown almost immediately after being dropped in the oil. Line a large plate with kitchen paper.
Return the dough to a floured surface and knead a few more times. Divide the dough into 6 balls and flatten each into a palm sized circle. Use your fingertips to coat the top of each ball with a little rapeseed oil.
Pop balls of dough into the hot oil 2 or 3 at a time, depending on the size of your pan. Fry them for about 30 seconds to 1 minute, then flip them over and cook until they are golden-brown on both sides and puffed up. Remove using a slotted spoon and place onto the lined plate to drain.
For the aioli, combine all the ingredients together in a bowl. Season, to taste, with salt and pepper.
To serve, slice open the fried bakes, spread liberally with aioli, stuff with the salt cod mixture, and top with slices of avocado.