Korean Fried Chicken Bao

Name: Korean Fried Chicken Bao
Prep time: 15 min
Cook time: 3 h
Total time: 3 h 15 min
Cuisine: Asian, Korean
Ingredients: 360g (12.6 oz) plain (all-purpose) flour, plus extra for dusting; 1 tsp baking powder; 1 tsp instant dry yeast; 35g (1 oz) white sugar; 35g (1 oz) vegetable oil, plus extra for greasing the dough; 180g (6.3 oz) warm water; 20ml milk; vegetable oil, for greasing; 4 large chicken thigh fillets, cut into bite-sized pieces; 2 tsp sea salt; ¼ tsp ground black pepper; 1 cup corn flour (cornstarch); vegetable oil for deep frying; 1 tsp sesame seeds; thinly sliced cucumber, to serve; 1/3 cup soy sauce; 1/3 cup sugar; 2 tbsp apple cider vinegar; 2 tbsp gochujang*; 2 tbsp tomato ketchup; 3 garlic cloves, finely chopped