Combine 1 tbsp hot water and red vinegar in a very small bowl with 1 tbsp currants.
In another very small bowl, toss champagne vinegar with the sliced shallot.
Wash and dry the leaves of watercress and mound on a large platter.
Cut the Blue Castello into small pieces, removing any rind, and strew over leaves.
With a very sharp knife cut the top and bottom off the grapefruit. Cut off all the rind and pith. Over a medium sized bowl, carefully slice between the membranes to remove the fruit in sections, catching any juice and the fruit in the bowl.
Arrange the sectioned grapefruit over the salad.
Toss the walnuts over the top.
Lift the shallots out of the vinegar carefully, reserving the vinegar for the dressing. Pulling the rings apart, scatter the shallots over the salad.
Drain the currants, and toss over the salad.
Add 1-2 tbsp grapefruit juice to the small bowl with the champagne vinegar. Whisk in olive oil, 1/2 tsp sea salt, and a few grindings black pepper. Dress the salad - you may not need all the dressing.
Preheat the oven to 325.
Toss all ingredients together in a medium sized bowl.
Lightly spray a rimmed cookie sheet with vegetable oil.
Spread the coated nuts over the cookie sheet.
Toast for 15 minutes, stirring every 5 minutes.
Remove from oven and cool stirring every few minutes so they don't stick too badly to the pan.