Combine all tartar sauce ingredients, except capers, in a small bowl. Reserve.
Combine flour, cornstarch, baking powder and salt in a small shallow bowl. Remove 1/2 cup of flour mixture and whisk together with 4 ounces of beer in a separate bowl. Reserve.
Heat 3-inches of oil in a deep pot to 375 degrees.
Using a small wire mesh strainer, lower capers into oil and fry for about 30 seconds. Remove to paper towels to drain; then stir into tartar sauce, reserving a few for garnish.
Fry pre-boiled potato slices in batches until golden brown. Remove to paper towels to drain.
Dredge fish nuggets in dry flour mixture and then in beer batter. Fry in batches until well browned, 2-3 minutes per batch. Remove to paper towels to drain.
To serve, place potato 'chips' on plate, add a teaspoon of tartar sauce and a battered fish nugget to each. Skewer through layers and sprinkle with crispy fried capers.