Step 1

A deep-fry thermometer

Step 2

Corn flour, which is more finely ground than cornmeal, is available at Latin markets, natural foods stores, and bobsredmill.com.

Step 3

Whisk egg yolk and 1 Tbsp. vinegar in a small bowl. Whisking constantly, slowly drizzle in oil, drop by drop at first, until mayonnaise is thickened and smooth. Add remaining 1 Tbsp. vinegar; season with salt and pepper. Cover and chill.

Step 4

Mayonnaise can be made 1 day ahead. Keep chilled.

Step 5

Fit a large pot with thermometer; pour in oil to measure 3”. Heat over medium-high heat until thermometer registers 375°.

Step 6

Meanwhile, whisk all-purpose flour, baking powder, baking soda, 1 tsp. kosher salt, and ½ tsp. pepper in a large bowl. 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).

Step 7

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° between batches, fry fish until golden brown and crisp, about 2 minutes per side. Transfer to paper towel–lined baking sheet.

Step 8

Season fish and fries with Old Bay, sea salt, and dill; serve with malt vinegar mayonnaise and lemon wedges.

Step 9

*Raw egg is not recommended for infants, the elderly, pregnant women, people with weakened immune systems…or people who don't like raw egg.