Thinly slice the 3 red onions on a cutting board.

Add 150 ml water and 100 ml apple cider vinegar to the small saucepan.

Add 50 g sugar and the pinch of salt to the saucepan.

Add the 2 thyme sprigs and 1 bay leaf to the saucepan.

Bring the pickling liquid to a boil on the stovetop.

Add the sliced red onions to the boiling liquid.

Bring the liquid back to a boil and turn off the heat.

Let the pickled onions and brine cool completely.

Measure 100 ml red onion pickle brine into a clean small saucepan.

Add 1 g agar-agar and stir until evenly dispersed.

Bring the brine mixture to a boil on the stovetop.

Simmer for 30 seconds while stirring continuously.

Immediately pour the hot liquid into the small flat mold.

Refrigerate the mold for at least 30 minutes until fully set.

Blend the set jelly until completely smooth.

Transfer the smooth gel into a pipette bottle for plating.