Layered Southwestern Salad

I received this recipe in an email forward from Sara Snyder, but I think it might have originally came from Beth Fullerton:

1/3 c. chopped fresh cilantro
1/2 c. lime juice
1/2 c. olive oil
1/2 c. sour cream
4 tsp. sugar
1/2 tsp. salt
1/2 tsp. pepper
1 large head romaine lettuce, torn into bite sized pieces
3 plum tomatoes, chopped
1 15 oz. can black beans, rinsed and drained
1/4 c. purple onion, chopped
1/2 bag (8 oz.) shredded Mexican 4-cheese blend
1 15 oz. can whole kernel corn with red and green peppers, drained
1 c. crushed tortilla chips

Process first 7 ingredients in a blender or food processor until smooth, stopping to scrape down sides. Layer lettuce and next 7 ingredients in a 3-quart glass bowl. Pour vinaigrette over salad just before serving, and gently toss.
(I didn't layer the salad because it had to be tossed anyway before serving.)

Yield: 8-10 servings