Directions

1. Preheat oven to 400°F with racks in upper and lower third positions. Combine chopped sweet potatoes with 2 tablespoons oil, 1 teaspoon each cumin, smoked paprika and taco seasoning and ½ teaspoon salt on a large rimmed baking sheet; toss until coated. Roast on the lower rack, tossing once, until browned and fork-tender, 20 to 25 minutes. Cover with foil to keep warm.
2. Meanwhile, brush both sides of tortillas with 1 tablespoon oil and sprinkle with ¼ teaspoon salt. Arrange on a large rimmed baking sheet (it’s OK if they overlap a bit; they will shrink as they cook). Bake on the top rack, turning once, until browned and crisp, 12 to 13 minutes. Transfer the tostadas to a wire rack and let cool.
3. Heat the remaining 1 tablespoon oil in a medium saucepan over medium heat. Add half of the chopped white onion; cook, stirring occasionally, until softened, about 3 minutes. Add chopped garlic, ¼ teaspoon salt and the remaining 2 teaspoons taco seasoning; cook, stirring constantly, until fragrant, about 30 seconds. Stir in undrained black beans and 6 tablespoons broth; bring to a simmer over medium heat. Mash the beans, using a fork or a potato masher, until smooth. Continue to simmer, stirring occasionally, until thickened, about 8 minutes. (There will be a few unmashed beans, that’s OK.) Remove from heat and cover to keep warm.
4. In a medium bowl, combine chopped tomatoes, red onion, cilantro and jalapeño, the remaining chopped white onion, 3 tablespoons lime juice, ½ teaspoon pepper and the remaining ½ teaspoon salt; mix well.
5. Top the tostadas with beans, sweet potatoes, tomato mixture and 2 tablespoons crema. Serve with lime wedges, if desired, and with the remaining tomato mixture on the side.