The official kickoff of Dungeness crab season in the San Francisco Bay Area is the second Tuesday of November and it's an occasion worth celebrating! You will need several round ring molds (2" wide x 3" tall) which you can purchase online or at a cooking store. Once you invest in the rings, you will discover many other uses for them. —Lynda Marren
To make the vinaigrette: Combine all of the ingredients except the olive oil. Slowly add the olive oil in a steady stream while whisking until smooth and emulsified. Set aside.
Cut the avocados in half lengthwise, remove pit and peel. Cut avocado into 1/4" pieces and place in a flat casserole dish in a single layer. Drizzle with about 1/3 of the vinaigrette and sprinkle with salt and pepper. Set aside.
Place crab in a small bowl and add another 1/3 of the vinaigrette. Add the parsley and thyme. Add more salt, pepper and cayenne to taste. Mix in just enough creme fraiche to bring the crab mixture together.
Slice the tomatoes 1/4" thick. Sprinkle with salt and pepper. Toss the butter lettuce and watercress with the remaining vinaigrette and set aside.
To build the tower: Put a ring mold in the center of each salad plate. If using tomatoes, place a sliced tomato in the bottom of each ring. Using a slotted spoon, transfer avocado to the tower and fan the avocado over the tomatoes. Top with a heaping amount of crab and gently push ingredients together. Fan the lettuce mixture around each tower. Carry salad plate to the table with the rings before gently removing the rings. Garnish with fresh herbs.