Rich and Creamy Tonkotsu Ramen Broth Recipe

Name: Rich and Creamy Tonkotsu Ramen Broth Recipe
Ingredients: 3 pounds pig trotters, split lengthwise or cut crosswise into 1-inch disks (as your butcher to do this for you); 2 pounds chicken backs and carcasses, skin and excess fat removed; 2 tablespoons vegetable oil; 1 large onion, skin on, roughly chopped; 12 garlic cloves; One 3-inch knob ginger, roughly chopped; 2 whole leeks, washed and roughly chopped; 2 dozen scallions, white parts only (reserve greens and light green parts for garnishing finished soup); 6 ounces whole mushrooms or mushroom scraps; 1 pound slab pork fat back