Pre-heat oven to 350 degrees F.
Bake potatoes on a tray in hot oven for 30 to 45 minutes - until knife tender. This can be done the night before or ahead of time. Cut each potato into 6 or 8 wedges depending on the size. Heat 3 inches of oil in a deep fryer. Or you can heat 3-inches of oil in a deep pot. Begin by frying half the wedges at a time for 4 to 5 minutes until crispy and brown. Drain on paper towels and season with salt.
In a large mixing bowl, combine the flour and cornstarch. Season the flour mixture with salt and fresh ground black pepper. Make a well in the center and gradually pour in the club soda and egg yolks whilst whisking. Work your way from the center out slowly combining the dry ingredients to form a smooth batter. Lightly coat the fillets of fish in seasoned flour then dip in batter and fry in 375 degree F oil. Fry for 4-5 minutes until crispy and golden brown. Remove and drain on paper towels, then season with salt. Serve with crispy fried parsley leaves and lemon wedges.
Prepare the tartar sauce:
In a small mixing bowl, combine all the tartar sauce ingredients. Set aside in the refrigerator for 10 to 15 minutes before serving, to let the flavors come together.