Prepare cornbread per instructions on package and cool. Divide into thirds.
Prepare the dressing using 1 ⅓ cup of milk or buttermilk and 1 cup of mayo. Whisk until fully combined, then chill until assembling the salad.
Prepare pico de gallo: In a medium size mixing bowl, toss together diced tomatoes, onion, and jalapeno pepper. Add chopped cilantro, lime juice and season with garlic salt and pepper to your taste. Chill until assembling.
Divide the ingredients into thirds. Layer in this order...shredded lettuce, crumbled cornbread, bacon, corn and black beans, pico de gallo, a drizzle of dressing and shredded cheese. Repeat until all of the ingredients are used.
Reserve some pico de gallo, bacon crumbles, and cheese to garnish the top. Dollop plain sour cream on top as a garnish.
Refrigerate for several hours, or preferably overnight to allow the flavors to come together before serving.