To make the tomato spaetzle with vongole, first mix the ingredients for the spaetzle with a wooden spoon to form a thick paste. In a wide pot, bring plenty of salted water to a boil. Place spaetzle dough in a spaetzle press and press into the boiling water. Stir gently with a wooden spoon and let sit for 1 minute. Lift out of the water with a strainer, rinse in cold water and then drain well.
Heat olive oil in a wide pot and sauté the root vegetables in it. Add diced tomatoes, garlic and vongole, sauté briefly and then deglaze with white wine. Cover and simmer for about 4-5 minutes. Season with salt, pepper and 2/3 of the basil, mix well.
Warm the spaetzle in a little olive oil, add the mussels and some of the broth.
Pour the tomato spaetzle with vongole into deep plates and serve sprinkled with pecorino and the remaining basil.