For the chicken, mix together the chicken stock, lemon zest and juice, sherry and garlic clove in a large casserole. Bring to the boil, then reduce the heat until the mixture is just simmering.
Add the chicken breasts and cover the casserole with a lid. Cook for 20-25 minutes, or until cooked through. Set aside to cool slightly.
For the lemon sauce, bring the chicken stock, sugar and lemon zest and juice to the boil in a pan, then continue to cook for 4-5 minutes.
Whisk in the cornflour paste until the mixture is smooth. Season, to taste, with salt and freshly ground black pepper.
Heat the butter in a frying pan over a medium heat. Add the cooled chicken breasts and fry for 2-3 minutes on each side, or until golden-brown on both sides.
To serve, place one chicken breast onto each of four serving plates. Pour over the lemon sauce. Spoon a portion of egg-fried rice alongside. Sprinkle over a little spring onion.