How to Make It
Preheat broiler to low with oven rack 8 inches from heat. Set aside 1 tablespoon chopped onion for garnish. Heat oil in a medium saucepan over medium. Add garlic and remaining 7 tablespoons onion; cook, stirring often, until softened, 3 to 5 minutes. Stir in cumin, chili powder, and salt; cook, stirring often, 30 seconds. Whisk together evaporated milk and cornstarch in a bowl. Add milk mixture to onion mixture; cook, stirring often, until bubbly and thickened, about 4 minutes. Add sweet potato; whisk until smooth. Fold in diced tomatoes and chiles and half of cheese.
Spoon mixture into a shallow 3- to 4-cup baking dish. Sprinkle with remaining half of cheese. Broil in preheated oven until cheese melts, about 2 minutes. Garnish with reserved chopped onion and, if desired, jalapeño and cilantro. Serve warm with assorted dippers.