Chop up the rhubarb and transfer, along with the cleaned roselles, to a heavy saucepan or pot.

Add enough water to cover, plus 2 cups more and allow to boil until the rhubarb/roselles are soft and the rhubarb is easily mashed with the back of a wooden spoon.

Strain the liquid through a layer of cheese cloth or a fine-meshed strainer, using a spoon to mash the solids and get as much juice out as you can.

As you return the liquid to the pan, measure it in cups. Add an equal measure of sugar or a bit less as you prefer.

Return to heat and mix until the sugar is completely dissolved.

Let the mixture come to a rolling boil, then turn off the heat.

Allow to cool, bottle, and store in the refrigerator.

You'll want to use the syrup up in a couple of weeks.

If you're using egg whites, do a "dry shake" first: shake all ingredients in a cocktail shaker without ice. Then add ice and shake once more. Serve on the rocks or "up" (without ice).

If you're not using egg whites, just skip the dry shake and get to it!

For non-alcoholic versions, simply pour the rhubarb-roselle syrup into a tall glass. Follow with ice, then top with either chilled tonic water or soda