Black Bean and Corn Burritos With Tomatillo Salsa

1 can (15 ounces) black beans, drained and rinsed1 1/2 cups corn kernels 1/2 teaspoon cumin3 cups shredded cheddar or Monterey jack cheese4 large flour tortillas8 tomatillos, husks removed, washed1 medium red onion2 garlic cloves 1/2 cup fresh cilantro leaves, lightly packed1-2 fresh jalapeno peppers (or 1-2 tablespoons pickled jalapeno slices), to taste1 small green apple, cored and cut into chunks 1/2 teaspoon salt 1/4 teaspoon freshly ground black pepper2 tablespoons extra-virgin olive oil3 tablespoons cider vinegar1 avocado, pitted, peeled and cut into thin slices1 cup sour creamHeat oven to 400 degrees. Line a baking sheet with foil and set aside.In a medium bowl, combine the beans, corn, cumin and 1 cup of cheese and mix well.Set a flour tortilla on a flat surface. Spread a fourth of the bean and corn mixture in a line down the center, leaving about 2 inches of tortilla bare on either end.To roll the tortilla, fold over either end, then wrap the sides up. Flip the burrito so that it lies flat on the folds, keeping them in place. Repeat with remaining tortillas.Transfer the filled burritos to the baking sheet. Top with the remaining cheese, then bake for 15 minutes, or until cheese is melted and lightly browned.While the burritos cook, prepare the salsa. In a food processor, combine the tomatillos, onion, garlic, cilantro, peppers, apple, salt, pepper, oil and vinegar. Pulse about 15 times or until salsa is chunky. Transfer to a bowl and set aside.When the burritos have finished cooking, use a spatula to transfer them to serving plates. Top each with avocado slices, a large dollop of sour cream and salsa.Serves four.