In a small food processor or using an immersion blender, combine the extra virgin olive oil, white wine vinegar, Dijon mustard, Roquefort bleu cheese, lemon juice, and minced garlic. Blend until well combined and creamy. Place dressing into a small bowl and refrigerate for at least 30 minutes.
While dressing is setting up in the refrigerator, rinse and dry the lettuce heads.
Slice each head in half lengthwise. Arrange on a large platter, leaving an open area for the grapes, candied walnuts, and the platted dressing.
Place the sliced seedless red grapes in an empty section of the platter and arrange the candied walnuts next to them.
At this point, the entire platter can be refrigerated until you’re ready to serve.
When ready to serve, remove the chilled dressing and scoop the desired amount into an empty area of the platter, close to the sliced grapes and candied walnuts.
Sprinkle extra crumbled bleu cheese over the dressing to garnish, then serve.