Select the best watercress stalks, cover them with wet paper and put in the refrigerator. Season the cherry tomatoes with olive oil and salt, then roast them in the oven for twenty minutes at 200°C. Boil 1 liter of lightly salted water, blanch the watercress for 1 minute and cool down immediately by pouring it into a bowl filled with water and ice. In a saucepan brown the shallot and some finely chopped potatoes, then cover them with water left from blanching the watercress and cook for 10 minutes. Add the watercress and blend everything until you get a smooth and creamy consistency. Toast the rice with a drizzle of olive oil and a pinch of salt, the pour in some slightly salted water and cook on a moderate heat for 5 minutes. Add some water and the watercress cream to the rice and cook for another 6 minutes. Cut the stracciatella into small pieces and season with a bit of olive oil and some ground pepper. Add the remaining cream to the risotto and turn off the heat. Season with parmesan cheese, pepper and a drizzle of olive oil, cover with a lid and let it rest for a couple of minutes. Plate the risotto with some fresh watercress, roasted tomatoes and stracciatella.