Fill a tall glass pitcher with olive oil and place it into the freezer for 30 minutes.
In a heat-proof bowl or jar, place sliced red onions.
In a small saucepan over medium high heat, bring the vinegar, sugar, and water to a boil.
Pour the boiling liquid over the slice red onions and wrap tightly, set aside for 30 minutes to overnight.
When onions are cool, drain 17 3/5 ounces (500 g) of the pickling liquid to a pot.
Add the pickled red onions to a jar and top with the remaining liquid. Reserve for future use.
Bring onion liquid to 194 F (90 C).
Stir the agar agar into the heated liquid and remove from heat.
Cool only slightly.
Pull the warm liquid into a kitchen squirt bottle or a meat basting syringe.
Working quickly, while the liquid is still warm, lightly drip liquid into the cold olive oil to form onion pearls.
Try to keep the onion pearls an equal size.
When finished, remove onion pearls from the olive oil with a slotted spoon or mesh strainer and rinse them in water.
Serve onion pearls with grilled and chilled potato slices, crème fraiche and chives (optional) or as a garnish for freshly shucked oysters on the half shell (optional).