Assembly:
- Remove core end from endive. Split in half. Remove inner core. Separate leaves. Place endive in bowl of ice water with 2 Tsp. of salt to soak for 30 minutes (soaking endive in salted ice water removes bitterness). Remove, roll in paper towels, and place in fridge to crisp.
- Cut avocado in half. Remove seed. Scoop from shells with large spoon. Slice into approximately 1/4" slices. Do not prepare avocado too soon or it will brown. Prepare and slice just before serving the salad.
- Slice red onion into very thin slices.
- Place wine vinegar, meaux mustard, salt, sugar, and pepper in small bowl. Whisk to blend well. Slowly drizzle in oil whisking continuously until oil is incorporated into mustard mixture.
- Arrange endive leaves on plates, top with tomato, avocado and onion slices. Drizzle with meaux mustard vinaigrette. Season with sea salt and fresh ground pepper.
*This dressing is delicious tossed with diced cold roasted potatoes, chopped cooked chicken breast, green onions, diced avocado, and sliced grape tomatoes for a tangy chicken, potato salad.