Roasted Sweet Potato and Poblano Nachos With Guacamole Recipe

Name: Roasted Sweet Potato and Poblano Nachos With Guacamole Recipe
Ingredients: 2 pounds sweet potatoes, peeled, cut into 1-inch cubes; 2 poblano chilies; 2 serrano chilies; 2 medium garlic cloves, unpeeled; 2 tablespoons canola oil; Kosher salt; 1 (16-ounce) can refried black beans; 1/4 cup chicken stock; 3 avocados; 1 tablespoon fresh juice from about 1 lime; Handful fresh cilantro, stems removed, leaves chopped; 1 bag of tortilla chips; 8 ounces Oaxacan cheese, or other string cheese (Monterrey Jack will only do in a pinch)