In a mixing bowl, mix together mayonnaise, salt, pepper, garlic powder, sugar, lemon juice, capers, dills, parsley, lemon zest, and yellow mustard until very well combined. Taste and adjust. Transfer the tartar sauce in an air-tight container and keep it in the fridge.
Heat the cooking oil in a wok over medium heat for about 8 minutes.
Cut one lemon into wedges and remove the seeds.
Pat dry the fish with a kitchen towel. Optionally, cut it in half to fit the serving plates.
Sprinkle 1 tsp of salt all over the fish fillets in 2 parts, and gently pat them to distribute the salt evenly on both sides.
Make the flour batter and flour coating. Transfer 60g (or half) of the crispy flour onto a plate and set it aside. Add the rest of the flour to a mixing bowl, along with cayenne pepper powder and a pinch of salt. Mix thoroughly with a whisk until combined. Add 60ml of iced water gradually in 25ml increments, mixing thoroughly until a wet, thin batter is achieved. Set it aside.
Place the fish, dry flour and flour batter next to the wok. Dip a pair of wooden cooking chopsticks into the oil. If bubbles form at the tips, it is ready for deep frying.
Coat one fish fillet with dry flour thoroughly all around, before shaking off the excess flour. Dip the fillet in the wet batter next, coating it generously. Shake off the excess batter, and carefully submerge it completely in the hot oil. Repeat with the rest of the fillets, until finished or there is no more space in the wok. Ensure that none of the fillets are not overlapping each other.
Fry the fillets for 5 minutes on one side. Carefully separate them if they get stuck to each other. Flip to the other side, and continue to cook for another 5 minutes, or until golden brown and crispy. Remove them from the hot oil, shaking them to drip off excess oil. Transfer to a cooling rack and set aside.
With a fine mesh strainer, strain and discard any and all the flour droplets in the oil.
Place the french fries into the strainer. Carefully lower the strainer into the hot oil. Let them fry for about 5 minutes. Then, continuously stir fry for 3-4 minutes, or until crispy and evenly golden brown.
Switch off the heat. Remove from the hot oil with a strainer and add them to a cooling rack lined with oil-absorbent paper. Sprinkle 1/8 tsp of salt over the fries and give them a light toss.
Place the fried fish fillet on the serving plate. Add a handful of french fries. Scoop about 1 tbsp of tartar sauce and place it on a saucer. Serve the fish and chips with the tartar sauce and 1 or 2 lemon wedges.