Pollo en Pipián Rojo de Nuez

Name: Pollo en Pipián Rojo de Nuez
Ingredients: 3/4 cup pecans, coarsely chopped; 6 chiles guajillos, stemmed and seeded; 3 chiles de árbol; 1 (1-inch) piece canela or cinnamon stick; 2 whole cloves; 1 tablespoon sesame seeds; 1/2 teaspoon cumin seeds; 2 tablespoons rendered lard, bacon fat, or extra-virgin olive oil; 3 pounds skin-on, bone-in chicken thighs; 1/2 medium white onion, chopped; 1 medium tomatillo, sliced; 3 garlic cloves, crushed; 1 tablespoon kosher salt, plus more to taste; 2 tablespoons grated piloncillo or dark brown sugar; 4 cups homemade chicken stock or low-sodium chicken broth; Cooked rice (for serving)