Blood Vessel Stew

Name: Blood Vessel Stew
Ingredients: Extra-virgin olive oil, for cooking; 1/2 pound chicken livers, cleaned; 2 onions, chopped; 2 carrots, chopped; 2 ribs celery, chopped; 1 bulb fennel, medium-diced; Kosher salt; 4 cloves garlic; 2 pounds ground beef; 1 pound sweet and/or spicy Italian sausage, casings removed; 1/2 pound beef heart, ground in a grinder on medium grind; 2 cups tomato paste; 3 cups hearty red wine; 10 to 12 sprigs fresh thyme, tied with kitchen string; 3 bay leaves; 1 pound ziti rigati; Grated Parmigiano-Reggiano, for serving