West African Peanut Soup with Chicken

Name: West African Peanut Soup with Chicken
Ingredients: 3/4 cup roasted and shelled peanuts; 2 tablespoons peanut or neutral oil, like grapeseed or corn; 1 medium red or white onion, chopped; 1 tablespoon minced fresh ginger; 3 cloves garlic, minced (1 tablespoon); 1/2 pound skinless, boneless chicken (about 2 thighs or breasts) cut into chunks; Pinch of cayenne; Salt and freshly ground black pepper; 6 cups stock or water; 2 sweet potatoes or yams (about 1 pound), peeled and cut into thick slices; 8 plum tomatoes, cored and halved (canned are fine; drain and reserve liquid for another use); 1/2 pound collards or kale, washed and cut into wide ribbons; 1/4 to 1/2 cup peanut butter, chunky or smooth