Heat the olive oil in a large skillet over medium heat. Add the onions and sauté until soft and translucent, about 5 minutes.
Stir in chipotle peppers and adobo sauce and cook for 2 minutes.
Add the can of black beans along with their liquid, the salt, garlic powder, chili powder, and cumin. Stir and continue simmering for an additional 3-4 minutes, then stir in the broth until well combined and bubbling.
Using a hand masher or immersion blender, mash the black bean mixture until it reaches your desired consistency. For a super smooth consistency, transfer the black bean mixture into a blender or food processor and blend until smooth.
Assemble and serve the tostadas by spreading a heaping 1-2 tablespoons of the black bean mixture onto your tostada shell. Sprinkle with shredded cheese or queso fresco and top with chopped cilantro, shredded lettuce, diced tomatoes, Mexican crema, and your favorite salsa.
Notes
Storage: Place the black bean mixture in an airtight container and refrigerate for up to 1 week. Store the toppings and tostada shells separately.
Reheating: Microwave the black bean mixture for 30 seconds to 1 minute until warm, then assemble your tostada as directed.
Keep the black bean mixture moist. Make sure to use the liquid from the can of black beans along with broth to keep the mixture creamy and spreadable.
Adjust the spice level. Keep the black bean mixture mild by using 2 extra tablespoons of adobo sauce in place of the actual chipotle peppers. To make it spicier, add chopped jalapeños.
Add protein. You can easily add more protein by topping your tostadas with ground beef, barbacoa, chicken tinga, or chorizo.
Assemble when you’re ready to eat. Tostadas have lots of toppings, so it’s best to assemble and eat them once you’re ready to keep the tostada shell from getting soggy.