How to Make It
Make the duck confit: Rub duck legs with 1/4 cup salt in a large, 3-inch-deep roasting pan. Cover and chill 8 to 12 hours.
Preheat oven to 225°F. Brush salt from duck legs, and rinse roasting pan. Arrange duck in roasting pan in a single layer. Pour fat over duck, and roast in preheated oven until duck legs are tender but not falling apart, about 3 hours. Let cool in fat at room temperature. Cover and chill 8 hours or overnight.
Make the ginger-leek broth: Combine 6 quarts water, duck bones, onions, leek, sliced ginger, and garlic in an 8-quart stockpot. Bring to a simmer over medium-high. Reduce heat to medium-low, and simmer 4 hours, skimming solids from top of stock for first 10 minutes of simmering. Strain and discard solids.
Make the arroz caldo: Bring 8 cups ginger-leek broth to a simmer in a large saucepan over high. Add brown rice and bring to boil, stirring occasionally. Reduce heat to medium-low to maintain a gentle simmer and cover. Simmer, stirring occasionally to prevent scalding, until rice is very tender and broth is thick, 1 hour to 1 hour and 10 minutes. Stir in fish sauce, 1 teaspoon kosher salt, and grated ginger.
Remove duck legs from fat, and scrape excess fat from legs. Reserve fat. Heat about 2 cups reserved duck fat in a 10-inch skillet over medium-high. Add 4 duck legs to pan; cook until skin is very crispy, 8 to 10 minutes. Flip duck legs, and cook until crispy, about 8 minutes. Remove from skillet and repeat with remaining 4 duck legs.
To serve, ladle 3/4 cup arroz caldo into each of 8 bowls. Place 1 duck leg, skin side up, in center of each bowl. In a medium bowl, combine pea tendrils, calamansi juice, and 1/8 teaspoon salt. Arrange dressed tendrils around duck legs over arroz caldo. Sprinkle each bowl with about 1 tablespoon fried garlic.