Here's a great make-ahead trick for this simple, colorful salad: A couple of hours before dinner, pour the prepared dressing into the bottom of the serving bowl, and assemble the salad greens on top. When you bring the salad to the table, all you need to do is toss--and you won't have soggy greens.
Combine shallots, vinegar, lemon juice, 1 tablespoon water, olive oil, mustard, sugar, salt, and black pepper in a large bowl, stirring well with a whisk. Add endive, radicchio, and arugula; toss gently to coat. Serve immediately.
Great salad. I've made it twice now and it was perfect each time. It's simple, low fat and fresh. I made it exactly as specified with the exception of topping each serving with a little shaved Parmigiano Reggiano.