Step 1

Preheat oven to 450°. Roast bones on a parchment-lined rimmed baking sheet 30 minutes. Arrange celery, onion, and carrots on sheet; roast 10 minutes. Spread tomato paste over bones and vegetables and roast 5 minutes more; let cool.

Step 2

Meanwhile, heat oil in a small saucepan over medium and cook garlic, shaking pan occasionally, until golden, about 5 minutes. Immediately strain oil through a fine-mesh sieve into a bowl; set aside garlic. Set aside oil for Ditalini Risotto and other uses.

Step 3

Transfer bones and vegetables to a large pot; pour in cold water to cover. Add herb stems, bay leaves, peppercorns, coriander seeds, and reserved garlic. Bring to a boil over medium heat. Reduce heat to low and simmer, skimming fat and foam from surface, until caramel colored and flavorful, about 3 hours. Strain stock through a fine-mesh sieve into a large bowl, pressing on solids; discard solids.

Step 4

Do Ahead: Stock can be made 3 days ahead. Let cool; cover and chill, or freeze up to 3 months.