Fish and Chips with Malt Vinegar Mayonnaise

Ingredients

• 2 teaspoons double-acting baking powder 
• 1 teaspoon baking soda 
• 0.5 teaspoon pepper black freshly ground plus more
• 1 cup seltzer water chilled
• 1.5 pounds haddock cut into long, 1 1/2"-wide strips
• 1 cup flour all-purpose
• 1 large egg yolk 
• 2 cups flour all-purpose
• 4 servings fries french (for serving)
• 1 teaspoon kosher salt plus more
• 12 ounces lager light chilled ()
• 4 servings lemon wedges (for serving)
• 1 tablespoon malt vinegar 
• 4 servings old bay seasoning fresh chopped (such as Maldon)
• 4 cups vegetable oil for frying

Equipment

• bowl
• baking sheet
• paper towels
• whisk
• pot
• kitchen thermometer

Directions

1. Whisk egg yolk and 1 tablespoon vinegar in a small bowl.
2. Whisking constantly, slowly drizzle in oil, drop by drop at first, until mayonnaise is thickened and smooth.
3. Add remaining 1 tablespoon vinegar; season with salt and pepper. Cover and chill.
4. DO AHEAD: Mayonnaise can be made 1 day ahead. Keep chilled.
5. Fit a large pot with thermometer; pour in oil to measure 3".
6. Heat over medium-high heat until thermometer registers 375°F.
7. Meanwhile, whisk all-purpose flour, baking powder, baking soda, 1 teaspoon kosher salt, and 1/2 teaspoon pepper in a large bowl.
8. Whisking constantly, slowly add beer, club soda, and vinegar, adding more beer if batter is too thick (it should be the consistency of thin pancake batter).
9. Place corn flour in a shallow bowl. Season fish with kosher salt and pepper. Dredge fish in corn flour, shaking off excess, then dip in batter, letting excess drip back into bowl. Working in batches and returning oil to 375°F between batches, fry fish until golden brown and crisp, about 2 minutes per side.
10. Transfer to paper towel-lined baking sheet.
11. Season fish and fries with Old Bay, sea salt, and dill; serve with malt vinegar mayonnaise and lemon wedges.