Step 1

Make the salsa fresca: In a medium bowl, combine the tomatoes, half of the dark green scallions, half of the minced jalapeño, 2 tablespoons of the lime juice, ¼ teaspoon of salt, and the sugar. (If your tomatoes are sweet, you can reduce or omit the sugar.) Set aside.

Step 2

Make the bean layer: Heat the olive oil in a medium skillet over medium heat. Add all of the light scallions and cook, stirring frequently, until softened, about 2 minutes. Measure out ¼ teaspoon of the minced garlic and set aside in a medium bowl (you'll use this for the guacamole). Add the remaining garlic to the skillet and continue cooking for 30 seconds more. Do not brown. Add the black beans, ½ teaspoon salt, ½ teaspoon of the cumin, and water and continue cooking for about one minute. Off the heat, mash the beans with a fork or potato masher until they have a chunky puréed texture. Scrape the beans into an 8-inch glass baking dish and spread into an even layer. Set aside. (The bean mixture may taste salty; that's okay.)

Step 3

Make the guacamole layer: To the medium bowl with the reserved garlic, add the avocados, the remaining dark green scallions, the remaining jalapeño, ½ teaspoon salt, the remaining ½ teaspoon cumin, and the remaining 2 tablespoons lime juice. Mash with a fork until blended but still a bit chunky.

Step 4

Assemble the dip: Spread the sour cream evenly over the black bean layer. Sprinkle half of the cheese over the sour cream, followed by all of the guacamole, and then the remaining cheese. Sprinkle the corn over the cheese.

Step 5

Transfer the salsa to a fine sieve and drain. Top the corn layer with the salsa. Serve the dip with a spoon and tortilla chips.