Add the diced chicken to a large mixing bowl and coat in the oil and seasoning. Add the cornflour and toss until the chicken is fully coated. You can add another tbsp or so cornflour if needed.
Air Fry (option 1): Lightly spray the base of the air fryer with oil. Spread the chicken out and lightly spray with oil. Cook at 200C/400F for 12 minutes, or until light golden, crisp and piping hot through the centre. You may need to work in batches.
Pan Fry (option 2): Add 4 tbsp oil to a large pan over medium-high heat (or enough to cover the base of the pan). Once the oil is hot enough that a crumb rapidly sizzles, spread out the chicken and fry each side for 3-4 minutes, or until golden, crisp and piping hot through the centre. You may need to work in batches. Place the chicken on a wire rack when done, then discard any excess oil and wipe out the pan.
For the sauce, add the sugar, butter, cream and soy sauce to a pan over low heat. Use a spatula to stir until everything is combined, with the sugar dissolved and butter melted. Increase the heat slightly and bring the sauce to a gentle simmer. Stir frequently for around 3 minutes or until the sauce thickens and starts turning syrupy. Keep in mind it'll thicken up more as it cools. You can add a pinch of salt if you think it needs it.
Turn off the heat and stir in the chicken until fully coated, then serve with sesame seeds and flaky sea salt.