Avocado-Tomato Stack

I've made the dressing for this two different ways so I'll include both.

Avocado-Tomato Stack with Cilantro-Lime Dressing
Serves 4

Ingredients:
1/3 cup fat-free milk
1 tsp. vinegar or lemon juice
1/4 cup chopped cilantro
3 tbsp. sour cream or plain yoghurt
1/2 tsp. lime zest
1 clove garlic, minced
1/4 tsp. sea salt
1/8 tsp. ground cumin
Dash of crushed red pepper flakes
4 medium tomatoes, sliced
1/4 cup red onion, very thinly sliced
1 small avocado
Freshly ground black pepper

Avocado-Tomato Stack with Lemon-Basil Dressing
Serves 4

Ingredients:
1/3 cup fat-free milk
1 tsp. vinegar or lemon juice
1/4 cup chopped fresh basil
3 tbsp. sour cream or plain yoghurt
1/2 tsp. lemon zest
1 clove garlic, minced
1/4 tsp. sea salt
1/8 tsp. dried oregano
Dash of crushed red pepper flakes
4 medium tomatoes, sliced
1/4 cup red onion, very thinly sliced
1 small avocado
Freshly ground black pepper

The method is the same for either dressing.
Method:
1. Make buttermilk by combining the milk plus the lemon juice or vinegar. Mix and then let this stand for 10 minutes. To make the dressing, add the buttermilk plus the next seven ingredients (through red pepper flakes) to the bowl of a food processor. Process 30 seconds or until well blended. Cover and chill.

2. Layer 1 tomato slice on each of 4 plates. Top each piece with a little red onion and some avocado. Repeat these layers three times, ending with avocado. Drizzle each stack with dressing and sprinkle with additional black pepper, if desired.

Reference:
Based on Heirloom Tomato and Avocado Stack from the June 2008 issue of Cooking Light.

My Changes:
*DIY buttermilk.
*Used additional sour cream in place of mayonnaise.
*Used full-fat sour cream (not low-fat).
*The lemon-basil dressing idea was suggested as a variation in the original recipe. However, when I tried it, I added in the oregano in place of the cumin called for in the cilantro-lime/original version.
*Used regular vine-ripened tomatoes (in this economy, you use what you have!) Would like to try it with fancier heirloom ones, though. :)