Blanch octopus for 1 minute. Drain, transfer to a small casserole, add oil, orange juice, sherry, vinegar, garlic, spices and bouquet garni, cover and simmer over low heat until very tender (1½-2 hours). Set aside to cool, then remove octopus from liquid and clean any skin or suckers from tentacles. Slice thickly crossways and set aside.
For tarragon aïoli, process yolks, garlic, vinegar and mustard in a food processor until smooth. With motor running, add combined oils in a thin steady stream and process until thick and emulsified. Season to taste with lemon juice and salt, thin with warm water, if necessary, then stir through tarragon.
Cook kipflers in boiling salted water until tender (15-20 minutes). Drain, cool, peel and thickly slice. Add tarragon aïoli, stir to coat and set aside.
For sherry dressing, warm sherry, vinegar and sugar in a small saucepan over low heat until sugar dissolves (2-3 minutes). Cool, add oil, season to taste and whisk to combine.
Heat a frying pan over medium heat. Add olive oil and chorizo and turn occasionally until crisp and golden (2-4 minutes). Set aside.
Combine octopus, lemon, shallot, chilli, mint and sherry dressing in a bowl. Divide potato mixture among plates, top with chorizo and octopus mixture and serve immediately.