Soak bread slices in water for about 2-3 minutes. Remove crust, squeeze remaining bread slices to remove excess water and place in a bowl.
Add chopped veal, pork, onions, parsley, mint, melba toast, eggs, lightly beaten, olive oil, salt and pepper to taste, and knead to combine. Cover bowl with plastic wrap and refrigerate for 30 minutes.
Preheat oven at 350 degrees F.
Remove the chopped meat mixture from the fridge. Mold pieces of the mixture into oblong shaped meatballs and place into a baking pan lined with parchment paper. Bake them in the preheated oven for about 15-20 minutes and reserve.
In the meantime we prepare the tomato sauce: In a hot saucepan, stir to sauté the onion, until caramelized. Add the tomatoes,olive oil. garlic, tomato paste dissolved in the vegetable broth, sugar, season with salt and pepper, and boil over medium heat for about 8-10 minutes, until the sauce lightly thickens.
Meanwhile, boil the tagliatelle pasta according to packaging instructions and drain.
Then add the "soutzoukakia" into the tomato sauce and simmer for another 3-4 minutes.
Serve "soutzoukakia" with the tagliatelle pasta.