Chicken Tamales

Name: Chicken Tamales
Ingredients: 2 (12-oz.) bone-in, skin-on chicken breasts; 1 large (12 oz.) white onion, halved; 4 garlic cloves, smashed; 1 tsp. whole black peppercorns; 4 tsp. kosher salt, divided; 6 cups tap water; 1 cup, plus 1 Tbsp. vegetable oil, divided; 1 (14 1/2-oz.) can diced tomatoes, drained; 2 to 4 Tbsp. chopped chipotle chiles in adobo sauce (from 1 [7-oz.] can); 18 dried corn husks; 3 cups masa harina; 1 tsp. baking powder; Toppings: salsa, pico de gallo, or sour cream