1) Preheat the oven to 200°C/gas mark 6. Line a baking sheet with parchment paper.
2) Place each chicken breast between two sheets of parchment paper or cling film and pound out to 1/2cm thick. Sprinkle both sides with salt and pepper.
3) Mix the flour, 1/2 tsp salt, and 1/4 tsp of pepper in a shallow plate. In a second plate, beat the egg and 1/2 tbsp of water together. Place the bread crumbs on a third plate. Dip each chicken breast first in the flour, shake off the excess, and then dip in the egg and bread crumb mixtures.
4) Heat 1 tbsp of olive oil in a large saute pan over medium to medium-low heat. Add the chicken breasts and cook for 2 minutes on each side, until browned. Place them on the baking sheet and allow them to bake for 5 to 10 minutes while you make the sauce.
5) For the sauce, wipe out the saute pan with a dry kitchen towel. Over medium heat, melt 1 tbsp of the butter and then add the lemon juice, wine, the reserved lemon halves, 1/2 tsp salt, and 1/4 tsp pepper. Boil over high heat until reduced in half, about 2 minutes. Off the heat, add the remaining 25g of butter and swirl to combine. Discard the lemon halves and serve one chicken breast on each plate. Spoon on the sauce and serve with a slice of lemon and a sprinkling of fresh parsley.