Squeeze the garlic paste from the heads of roasted garlic into a blender. Add the orange juice, mustard, vinegar, salt, and pepper and puree until smooth and creamy. Add the tarragon and whirl briefly just to mix-there should be flecks of green throughout the golden dressing. Set aside for at least 30 minutes to allow the flavors to marry. Tightly sealed and refrigerated, the dressing will keep for about a week.