Adjust rack to top position and preheat broiler to high (or oven to 500 degrees). Wash and dry all produce. Dice tomato. Chop cilantro leaves and stems, keeping them separate. Deseed and finely dice jalapeño. Zest and quarter lime. Halve, peel, and dice onion. Drain beans, reserving liquid in a small bowl.

In a medium bowl, combine tomato, cilantro leaves, half the jalapeño, juice from 2 lime wedges (4 wedges for 4 servings), and 2 TBSP onion (3 TBSP for 4 servings); season with salt and pepper. In a second small bowl, combine sour cream and lime zest (to taste). Stir in water, 1 tsp at a time, until mixture reaches a drizzling consistency. Season with salt and pepper.

Heat a large drizzle of oil in a medium pot over medium-high heat. Add remaining onion and cook, stirring, until softened, 2-3 minutes. Add beans, chili powder, and cilantro stems. Cook, stirring, until fragrant and thoroughly combined, 2-3 minutes. Add bean liquid and a pinch of salt. Cook until thickened, 4-5 minutes. Turn off heat; mash beans until mostly smooth.

Meanwhile, drain corn and pat dry with paper towels. (TIP: The drier your corn, the less likely it is to pop.) Heat a large dry pan over medium-high heat. Add corn and cook, without stirring, until browned on bottom, about 4 minutes. Add 1 TBSP Southwest Spice and a pinch of salt and pepper. Continue to cook, stirring, until browned all over, about 1 minute more. Turn off heat; transfer to a second medium bowl.

Place tortillas on a baking sheet. Drizzle on both sides with olive oil; rub all over to coat. Poke all over with a fork. Broil, flipping halfway through, until lightly browned, 1-2 minutes per side. TIP: Tortillas brown quickly! Keep a close eye on them.

Spread tortillas with beans. Evenly top with cheese, corn, salsa, crema, and remaining jalapeño (to taste). Serve with remaining lime wedges on the side for squeezing over.