Heat oven to 200C/fan 180C/gas 6. Put the flour in a large bowl with the saffron and some seasoning. Coat the chicken breasts in the flour mix, then shake gently to remove any excess.
Heat the olive oil in a large, heavy roasting tin, then quickly brown the chicken all over. Cover the tin with foil, then roast for about 20 mins until the chicken is crispy and golden, then removing the foil for the final 5 mins of cooking time.
Meanwhile, boil the potatoes in a large pan for about 15 mins or until tender, drain well, return to the pan, then mash. Place the pan back over a low heat, season, then mix in the milk and taleggio. Stir constantly, allowing the cheese to melt gently and create a smooth, creamy texture.
When the chicken is cooked, put the tray back on the hob and add the grappa and grapes. Warm through, then remove from the heat and flambé by lighting with a taper. When the flames die down, return to the heat and simmer for about 30 secs.
To serve, place 3-4 tbsp mash in the middle of each plate and sit a chicken breast on top, then spoon over the grapes and juice.