Filipino Oxtail Stew

Ingredients

1 1/2 pounds beef oxtail, cut into pieces
1 large onion, quartered
2 cloves garlic, chopped
1 teaspoon salt
1/2 teaspoon ground black pepper, or to taste
1 large eggplant, cut into 2-inch chunks
1/2 head bok choy, cut into 1-inch pieces
1/2 pound fresh green beans, trimmed and snapped into 2-inch pieces
1/4 cup peanut butter, or as needed to thicken sauce
Directions

Fill a large saucepan with water, and drop in the oxtail pieces, onion, garlic, salt, and pepper. Bring to a boil, and simmer for 2 hours over medium-low heat, skimming the foam occasionally, until the oxtail meat is very tender and the broth is reduced to 3 cups.
Stir in the eggplant, bok choy, and green beans, and simmer for about 20 minutes, until the vegetables are tender.
Just before serving, place the peanut butter in a small bowl and thin with 1 or 2 tablespoons of broth. Stir until smooth and add to the stew.