Chicken Tikka Masala

Name: Chicken Tikka Masala
Ingredients: 1 small onion; 1 2-inch piece of ginger; 4 cloves garlic; 1/4 cup plain yogurt; 1/4 teaspoon cayenne pepper; 1/4 teaspoon garam masala; 2 pounds boneless, skinless chicken breasts, cut crosswise into thirds; 2 medium red onions; 1 2.5-inch piece of ginger; 1/3 cup canola oil; 1 cinnamon stick; 1/2 teaspoon turmeric; 1 tablespoon coriander; 1 teaspoon cumin; 1/4 teaspoon cayenne; 1 1/2 lbs s tomatoes, puréed in a food processor, may substitute plain canned tomato purée; Salt to taste; 1/2 cup heavy cream; 2 tablespoons cilantro stems, optional