Whisk together the garlic, egg yolk and salt in a small bowl. Add the oil drop by drop to begin with, then more gradually, stirring constantly to form a thick aïoli. Stir in the lemon juice, season.
Mix the flour, cornflour and baking powder, combine with the mineral water to make a thin batter, season. Dip the fish fillets and mini octopus in the batter, shake off the excess batter.
To deep fry
Preheat the oven to 80°C. Line a baking tray with baking paper, place a rack on top, transfer to the oven. Heat the oil in a cooking pot to approx. 180°C. Deep-fry the fish fillets and mini octopus for approx. 6 mins. per batch until golden brown, keep warm on the rack. Serve with the lemon wedges, parsley and aïoli.