In a food processor, combine one ripe avocado, the juice of one lime, a clove of garlic, a handful of cilantro, and ⅓ cup of sour cream or yogurt. Blend until smooth, adding water a tablespoon at a time until you reach your desired consistency.

Heat your grill or a grill pan over medium-high heat. Place fresh sweet corn on the grill and cook for about 4 minutes until charred and tender. Set aside.

In a large skillet, heat olive oil over medium heat. Add chopped yellow onion and a pinch of salt, stirring frequently for 5 minutes until translucent.

Add minced garlic along with chili powder, cumin, and smoked paprika. Cook for another minute until fragrant.

Add two drained cans of black beans and cook for 4-5 minutes, stirring occasionally. Mash some of the beans for a creamy texture and stir in broth or water.

Squeeze the juice from the second lime into the bean mixture and adjust salt to taste.

Warm tostada shells in the oven at 350°F for 5 minutes. Spread the black bean filling on each shell, top with charred corn, and drizzle with avocado crema.

Serve immediately while crispy, garnishing with chopped cilantro or jalapeño slices.