Fried chicken and onions in a crispy breading

Ingredients:

• 2.5 kg chicken pieces with skin and bones (cut the breasts in half crosswise)
• 1.5 cups yellow mustard
• 8-10 sprigs of thyme
• 1 small onion, halved and thinly sliced ​​from root to tip
• Vegetable or peanut oil, for deep frying
• 5.5 tbsp. cake flour
• 2 tbsp baking powder
• 1 tbsp paprika
• 1 tbsp dried dill
• 0.5 tsp cayenne pepper

Preparation:

1. In a large bowl or wide saucepan, whisk the mustard with 2 cups of water until smooth; add the thyme sprigs. Add the chicken and onion, turning to coat thoroughly. Press firmly to coat the chicken. Cover and refrigerate for 2-4 hours.
2. Fill two 12-inch (30-cm) cast-iron skillets with about 2.5 inches (6 cm) of vegetable oil. Heat over medium heat until a deep-fry thermometer reads 350°F (175°C).
3. While the oil is heating, prepare the breading. In a large bowl, combine 3 cups of flour. Add 1/3 cup of the chicken marinade; stir until a crumbly mixture forms. Then whisk in the remaining 2.5 cups of flour, baking powder, paprika, dill, cayenne pepper, 1 tablespoon of salt, and 2 teaspoons of black pepper.
4. Working with a few pieces at a time, remove the chicken and onions from the marinade, drain any excess back into the bowl, and dredge in the flour mixture, pressing it with your hands to completely coat the chicken and onions. Transfer to a wire rack set on a rimmed baking sheet.
5. Carefully lower about 5 chicken pieces into each skillet, then adjust the heat so the oil temperature remains between 300°F and 315°F (150°C and 160°C). Cook, turning the chicken occasionally, until golden brown and crispy on the outside and cooked through, 15 to 16 minutes. A thermometer inserted into the meat should read 165°F (71°C) for breasts and 175°F (76°C) for legs and thighs.
6. Using tongs, transfer the chicken pieces to a clean wire rack set on a rimmed baking sheet and season with salt. Heat the oil again to 175°C and fry the remaining chicken. Then, fry the onion for 2-3 minutes, stirring occasionally. Transfer the chicken and onion to a platter.