Whip the cream just until firm peaks form. Stop before it gets any more firm. Too soft and the whipped cream will get watered down when added to the rhubarb.
The Fools can be assembled and stored in the fridge for a couple of hours before serving. If not serving right away, don't drizzle the syrup on until ready to go out.
If baking the cookies on a humid day, you may find that the meringue doesn't come together, or that they don't completely cook through, and the insides are still sticky.
If this is the case, thoroughly warm the oven again at 350F, and put the cookies back in, and turn off the oven again. Check after 4 hours.
You will have more cookies than needed for the recipe. Just enjoy!