Wash the guinea fowl, pat dry and carefully remove the skin from the breast, forming pockets with your fingers between the breast flesh and the skin.
Cut the truffles into thin slices and strips, fill the truffle pieces into the guinea fowl pockets and distribute evenly. If you don't get any truffles, please follow the instructions for herbs as a filling. Season the guinea fowl with salt and pepper.
Preheat the oven to about 230 degrees Celsius, add hot air to the guinea fowl, then reduce the temperature to about 190 degrees Celsius.
Cut potatoes into cubes (1cm), then brown lightly in butter. Deglaze with chicken stock and bring to the boil.
To flavour the potatoes, add some garlic and parsley stalks and cook over a moderate heat until al dente.
Finely chop a few parsley leaves, add to the potatoes and bring to the boil again. If necessary, extend the reduced stock with a little chicken stock.
Remove the guinea fowl, cut into pieces and carve. Add the potatoes and stock to the roaster, stir gently and combine the flavours of the gravy with the potato stock. Arrange the potatoes and stock, place the truffled guinea fowl breast on top and serve.