In a small saucepan, combine the rhubarb, water and sugar. Heat over a low flame, stirring occasionally. Once the rhubarb is soft, crush it with a potato masher and continue to simmer very gently for about 5 minutes, or until the rhubarb is broken down completely and fairly thick. Remove the stewed rhubarb from heat and strain the solids out (you can press on the solids with the back of spoon or the potato masher to speed the process up). Do NOT discard the solids. Set everything aside to cool.

Once the rhubarb solids have drained and cooled enough to touch, combine them with the red wine vinegar and let sit for 10 minutes or so. After the time has elapsed, give the rhubarb a squeeze or press on it with a spoon to extract the rhubarb-flavoured vinegar. Combine the liquid with the juice from step 1.

Measure the juice and red wine vinegar extracts - you should have a little over 1/4 cup. If you have more than this, either increase the other ingredients in the recipe or set a little aside.

Combine the juice/vinegar extract with the Dijon mustard and lemon juice and start slowly whisking in the olive oil. Whisk vigorously until the vinaigrette is glossy, thick, and well-combined.

Add the poppy seeds and black pepper and whisk briefly to combine. The vinaigrette can now be used, or stored in the fridge for up to a month. If the dressing separates in the fridge, allow it to come to room temperature then shake vigorously to recombine.