In a medium bowl, combine chopped parsley, tarragon, minced shallots, cornichons, crumbled hard-boiled egg yolk, diced egg white, white wine vinegar, a pinch of salt, Dijon mustard, and mayonnaise. Mix well until all ingredients are fully integrated.

Let the tartar sauce sit at room temperature while you prepare the beer battered halibut.

In a large mixing bowl, sift together the cake flour and baking soda until fully combined.

Gradually whisk in the cold beer, mixing gently until the batter is smooth and lump-free.

Allow the batter to rest for about 15-20 minutes.

Pour vegetable oil into a deep pan, filling it up to 2 inches. Heat over medium-high until it reaches 350°F (175°C).

Check if the oil is ready by dropping a small spoonful of the batter into the oil.

Pat the halibut fillets dry with paper towels and season both sides with salt.

Dip each seasoned halibut fillet into the batter and allow excess to drip off.

Carefully lower the fillets into the hot oil and fry for about 4-5 minutes per side until golden brown.

Remove the fried halibut from the oil using a slotted spoon and place them on a paper towel-lined plate.

Serve the beer battered halibut immediately with homemade tartar sauce, crispy fries, and coleslaw.