Cut chicken into small, even 1/2-inch cubes (small!)
Whisk milk and vinegar in a bowl and let sit 5 minutes. Add egg and salt and whisk until smooth. Add chicken and toss to coat. Cover and refrigerate at least 1 hour, up to 8 hours.
In a large shallow bowl, whisk together all breading ingredients. Remove 3 tablespoons of the marinade and drizzle over the flour mixture. Use fingers to mix until small clumps form.
Add peanut oil to a large heavy-bottomed pot. Heat over medium-high to 350°F, using a thermometer to monitor temperature (very important!). Line a plate with paper towels.
Using tongs, transfer chicken from the marinade into the breading, scattering across the surface. Gently toss to coat, then press the flour mixture onto the chicken to create craggy pieces. Shake off excess.
Carefully lower chicken into hot oil in batches. Do NOT overcrowd the oil; only about 8-10 pieces at a time or in a single layer. Fry 2 to 3 minutes, until golden brown and cooked through. Stir halfway through to separate pieces.
Use a metal strainer or slotted spoon to remove chicken. Let drain on paper towels. Lightly sprinkle with salt if desired. Serve immediately with sauce (see below).
Make sauce: In a small bowl, whisk mayo, mustard, honey, and BBQ sauce. Add 3/4 teaspoon lemon juice. Season with a pinch of salt and pepper (about 1/4 teaspoon salt and 1/8 teaspoon pepper). Taste and adjust as needed.
Video
Notes
Storage: Best right out of the fryer. If you have leftovers, let nuggets cool completely, then store in an airtight container in the fridge for up to 3 days. Reheat in an air fryer or oven at 375°F until warmed through and crispy again. Avoid the microwave, it makes them soft.