You don’t have to wait for the Double Decker Chicken Burger, a copycat version of the McDonald’s UK sandwich, to come to the US. You can make this much-loved British trend at home!
In a medium bowl, whisk together all of the sauce ingredients until well combined. Cover the bowl tightly with plastic wrap and chill in the refrigerator until needed.
In a large bowl, stir together the egg, lemon juice, and club soda.
Whisk in the flour, cornstarch, Old Bay, and baking soda until a batter forms, but do not overmix. Place the bowl in the refrigerator.
In a large, deep skillet, pour enough oil into the bottom so that it comes 1-inch up the side.
Over medium heat, bring the oil up to 350 degrees.
Remove the batter from the refrigerator and dip each chicken cutlet into the batter, making sure that both sides are coated.
Add the chicken to the skillet. Do not overcrowd the pan or the chicken will be greasy. You may need to work in batches.
Cook the chicken until golden brown and crispy and no longer pink in the center. Turn the chicken after 7-8 minutes and cook the other side for another 5 minutes. The time may take more or less time depending on the thickness of your chicken cutlet.
Remove the chicken to a paper towel-lined baking sheet to drain.
Top each cutlet with a slice of American cheese.
In another skillet over medium heat, butter the insides of the buns and the middle bun and toast them in the skillet until golden brown. Set aside.
Spread the sauce generously on the buttered side of each bun part.
Top the bottom bun with shredded lettuce and pickles.
Place a chicken cutlet on top of the pickles, followed by the second bun bottom with sauce slathered on.
Add a bit more shredded lettuce and pickles.
Place another chicken cutlet on the second bun.
Place bun top on the chicken and gently compress the sandwich so that it holds together.
Serve the sandwich hot with fries or chips on the side.