For the saffron aioli, using a food processor or pestle and mortar, blend the egg yolk, saffron, mustard, garlic and the juice and zest of the lemon.
Gradually add the light olive oil to the mixture and season with salt, to taste. Leave in the fridge until later.
Remove the tentacles from the defrosted octopus and cut into five pieces each. Discard the head and the bottom very thin part of the tentacles.
Preheat the oven to 170C/150C Fan/Gas 3.
For the cassoulet, add a generous pour of olive oil to a heavy-based casserole pan and add the onions and smoked paprika, season with salt and cook for 3 minutes.
Add the sausage, and cook for 2 more minutes. Add the beans, octopus pieces, chilli, garlic and tomatoes. Pour in the stock, which should be just under the level of the beans and octopus, add the bread pieces and cover with a cartouche (a circle of greaseproof parchment that covers the food). Bring to a simmer and place in the oven to cook for 1 and a half hours; remove the cartouche for the last 30 minutes.
Remove from the oven, allow to cool and strain the remaining liquid into a separate pan, reserving the cassoulet. Using a hand-blender, blend in a tablespoon of the aioli to the sauce and squeeze the cooked garlic out of the peel and into the sauce. Blend again and add the parsley.
Return the octopus, sausage pieces and beans to the sauce, warm through and serve with the remaining aioli on the side.