In a small bowl, whisk together the wine, vinegar, mustard and shallots in a small bowl. Slowly whisk in the oil and then the sour cream. Season to taste with salt and pepper.
ASSEMBLE THE SALAD:
To a medium bowl, add the watercress, endive and grapes, and drizzle with dressing; toss well to coat, then lightly stir in the avocado.
Transfer to salad plates and season with pepper.
Notes
If you are preparing this recipe as GLUTEN FREE, just be sure to use a brand of Dijon that is known to be GF.