Step 1

FOR THE CHICKEN: Set wire rack in rimmed baking sheet. In wide, shallow bowl, whisk together flour, cornstarch, pepper, cayenne, and baking powder. Drizzle buttermilk over flour mixture and mix with your fingers until combined and small clumps form. In medium bowl, whisk together eggs and salt.

Step 2

Working with 1 piece at a time, dip chicken in egg mixture and turn to coat. Lift from egg mixture, allowing excess to drip back into bowl. Coat both sides of chicken in flour mixture, pressing to form thick, bumpy coating. Place on prepared rack. Refrigerate, uncovered, for at least 1 hour or up to 8 hours. While chicken rests, make sauce and blue cheese spread.

Step 3

FOR THE BUFFALO SAUCE: Melt butter in small saucepan over medium heat. Add cayenne and cook, stirring constantly, until fragrant, about 30 seconds. Add hot sauce (mixture may sputter) and cook, stirring occasionally, until sauce is thickened and spatula drawn across bottom of pan leaves trail that takes longer than 5 seconds to fill in, 4 to 5 minutes. Remove from heat and stir in vinegar.

Step 4

FOR THE BLUE CHEESE SPREAD: In small bowl, mash blue cheese with fork until no pieces larger than ¼ inch remain. Add mayonnaise and continue to mash until incorporated. Stir in buttermilk and vinegar until combined. Refrigerate until needed.

Step 5

Place second wire rack in second rimmed baking sheet. Heat oil in large Dutch oven over medium-high heat to 425 degrees. Carefully transfer all chicken to oil and fry until chicken registers at least 155 degrees, 2 to 3 minutes. Transfer chicken to prepared rack. Using pastry brush, coat top of chicken with half of Buffalo sauce.

Step 6

Open buns on cutting board. Transfer 1 chicken piece, sauce side down, to each bun bottom. Brush remaining Buffalo sauce over chicken. Top each chicken piece with ½ cup lettuce. Spread each bun top with 2 teaspoons blue cheese spread. Invert bun top onto each sandwich and serve, passing remaining blue cheese spread separately.