1770 House Meatloaf

Name: 1770 House Meatloaf
Ingredients: 2 tablespoons good olive oil; 2 cups chopped Spanish onion (1 large); 1 1/2 cups small-diced celery (2 stalks); 1 pound ground beef; 1 pound ground veal; 1 pound ground pork; 1 tablespoon chopped fresh flat-leaf parsley; 1 tablespoon chopped fresh thyme leaves; 1 tablespoon chopped fresh chives; 3 extra-large eggs, lightly beaten; 2/3 cup whole milk; 2 tablespoons kosher salt; 1 tablespoon freshly ground black pepper; 2 1/2 cups panko (Japanese bread flakes); Garlic Sauce, recipe follows; 3/4 cup good olive oil; 10 garlic cloves, peeled; 2 cups chicken stock, preferably homemade; 3 tablespoons unsalted butter, at room temperature; Kosher salt and freshly ground black pepper