Cut away the fat that surrounds the two milker veal kidneys, cut them into pieces, put them to soak under a thread of running water and let them stay for 2 hours.
After that, letting them simmer a bit, without any dressings in a pan, let the kidneys get rid of their water, therefore drain them and put them aside.
Fetch a saucepan and, along with 7-8 tablespoons of extra-virgin olive oil, let 2 big red onions cut into slices simmer sprinkled with salt and pepper, for 10-12 minutes, stirring several times so it won't stick to the bottom and burn. At this point fetch the kidneys again and put them in the saucepan along with the onion and, still stirring often, on a medium heat, saucepan not lidded, let them cook for 7-8 minutes.
When the time is up stir and mix well with 1 nice glass of new red wine, increase the heat a bit, let it evaporate for 4-5 minutes, so it will all rather dry up and the taste will become concentrated. Add, at this point, ½ kg of fresh tomatoes (sweet the cherry type or Florentine, be sure they are not sour), thoroughly blended in the blender, again stir and mix it all very thoroughly, let it come to a boil again, lower the heat, cover with the lid, let it stew very slowly for 5-6 minutes stirring a few times. Now comes the time to also add 600 gr. of champignon mushrooms finely sliced, still stir well, let it slightly come to a boil, cover it with the lid and let it cook, keep it covered and stir 2-3 more times for 35-40 more minutes.
Afterwards taste it and, eventually, fix the salt and pepper, and then quickly serve it hot, dish and side-dish together.
Wine: perfect a vintage Rosso di Montalcino (to use also while cooking). Colour - intense ruby red; Scent - ample, fresh, of violet and vanilla; Taste - dry but full bodied and fruity with ample spicy scents.