Blend vinaigrette ingredients in a blender until smooth and form a loose paste.
Gently toss the spinach leaves in extra-virgin olive oil, salt, and pepper.
For a special presentation, Chef Boswell likes to spread the vinaigrette dressing (about 1/3 cup) on the bottom of the plate and arrange the grapes in a decorative pattern on top. The grapes can be left whole but, at his award-winning restaurant Stella!, Chef Boswell cuts the ends off of each grape so they are a uniform size and can be stood up on end in a checkerboard or mosaic pattern. The grapes are then garnished with the toasted walnuts and baby spinach leaves or other fresh greens.
*To toast walnuts: Place walnuts on a baking sheet and toast for 4 minutes at 350 degrees F. Gently crumble walnuts after they have cooled.
Optional: If a softer texture of grape is desired, blanch the grapes in boiling water for 7 seconds, then shock in ice water and peel gently.